President Bush could hardly have picked a more critical time to host China's President Hu Jintao at the White House.

A flare-up in troubled waters between South Korea and Japan, faltering trilateral cooperation among the US, Japan, and South Korea, and the failure to persuade North Korea to come close to terms on its nuclear-weapons program all make China a pivotal player -- while raising questions about US strength and influence in the region.

"The United States can play a more profound role in stabilizing the region," says Moon Jung In, international relations professor at Yonsei University in Seoul. "China may be happy to see what's happening."

While the United States tries to persuade China both to reduce its yawning trade surplus with the US and get North Korea to return to six-party talks, a potentially explosive quarrel between South Korea and Japan is frustrating Washington's efforts to join its two northeast Asian allies in common cause on the nuclear issue.

"High-ranking officials of the South Korean government have been talking about Korean-US cooperation rather than trilateral cooperation," says Kim Sung Han, director of North American studies at the Institute of Foreign Affairs and National Security, affiliated with South Korea's Foreign Ministry.

"Trilateral cooperation is vital to resolving the North Korean problem," he says.

The tendency in Korea is to blame Japan for somehow wishing to assert its own role in the region, reminding both Koreans and Chinese of the history of Japanese imperialism in Asia, culminating in the conquest of much of the Chinese mainland and 35 years of colonial rule over the Korean peninsula.

Who lays claim to islands?

Memories of that history have leaped into the headlines as a result of a stand-off midway between Korea and Japan in what Koreans call the East Sea and the much of the rest of the world knows as the Sea of Japan.

The focal point is a cluster of 34 islets, basically uninhabitable, that both Korea and Japan claim as part of their national territory.

Korea calls the cluster "Dokdo," or "Solitary Island," while Japan calls it "Takeshima," or "Bamboo Island," and Japan also wants to give Japanese names to undersea rock formations surrounding the islands, basically volcanic rock thrust up from the sea.

The issue, simmering for years, reached a boiling point this week when Japan said it was sending two survey vessels to chart the waters around the islands, held by a garrison of Korean troops seen on Korean television manning anti-aircraft weapons and machine-guns as if to stave off enemy invasion.

Eager to prove his fearlessness in the face of the Japanese, South Korea's President Roh Moo-Hyun has ordered 18 patrol boats to form a blockade against the survey vessels.

"Some people are claiming territorial rights to former colonies that were once acquired through war and aggression," he told Christian leaders at a breakfast Thursday. Not just "good will," he said, as if preparing for war, but "wisdom and courage" were needed in such a crisis.

Shinzo Abe, Japanese government spokes-man, says the vessels are going there in defiance of a pledge of "stern action" by Korea's foreign minister, Ban Ki Moon, against any "provocation" by Japan.

Mr. Kim, of the Institute of Foreign Affairs and National Security, accuses Mr. Abe, an outspoken conservative who aspires to succeed Junichiro Koizumi as Japan's prime minister, of playing to the right-wing in refusing to address Korean sensitivities.

"Shinzo Abe has his own agenda," says Kim. "The Japanese are trying to increase their own role in the area of security. This is sending conflicting messages."

The sense here is that the US could rein in Japan but is reluctant to do so while cooperating closely with Japan on North Korea.

"The United States has been rather silent on these issues," says Kim Tae Hwan, research professor at Yonsei University. "Koreans have been very uncomfortable with the Japanese posture of aligning with the United States. Japan seems to disregard expectations from Korea."

While playing into the hands of China, the standoff over the islands also comes at an opportune moment in terms of South Korea's policy of rapprochement with North Korea.

Ministerial talks between North and South

South Korea's unification minister, Lee Jong Seok, goes to Pyongyang Friday for the first ministerial-level talks between North and South Korea in five months. He and his North Korean opposite number will have no trouble agreeing on the need to fend off what North Korea has already denounced as a "shameless" attempt at expansion.

It's a "very clear win-win" for both North and South Korea, says David Kang, a professor at Stanford University's Shorenstein Asia-Pacific Research Center. In the process, he says, the ruckus at sea "makes it look a lot as if Korea and China are cooperating more since they're both upset by Japan's moves."

Mr. Kang sees the standoff as "a distraction" that probably will not have "a fundamental effect on North-South Korean relations," but adds to the sense that six-party talks on North Korea's nuclear weapons are not likely to go anywhere.

"The US doesn't expect to make any progress on six-party talks," says Kang. "Nobody has a face-saving way out."

Before attacking Iraq in March 2003, the United States told the world that Saddam Hussein had reconstituted his nuclear weapons program in defiance of the United Nations. That claim, used to justify the war, was based on assessments provided by the United States intelligence community. But as everyone now knows, those assessments were wrong. So Jeffrey T. Richelson's history of American nuclear intelligence, including our attempts to learn about Iraq's nuclear program, could hardly be more timely.

In "Spying on the Bomb," Richelson, the author of several books on American intelligence, has brought together a huge amount of information about Washington's efforts to track the nuclear weapons projects of other countries. He examines the nuclear projects of Nazi Germany, the Soviet Union, China, France, Israel, India, South Africa, Taiwan, Libya, Pakistan, Iran and North Korea, as well as Iraq. Through interviews and declassified documents as well as secondary works, he sets out briefly what we currently know about those projects and compares that with assessments of the time.

This may sound like heavy going, but Richelson writes with admirable clarity. And along the way he has fascinating stories to tell: about plans to assassinate the German physicist Werner Heisenberg during World War II; about discussions in the Kennedy and Johnson administrations on the possibility of attacking Chinese nuclear installations; about Indian measures to evade the gaze of American reconnaissance satellites; and about the bureaucratic infighting over the estimates on Iraq.

The United States has put an enormous effort into gathering information about the nuclear projects of other countries. After World War II it equipped aircraft with special filters to pick up radioactive debris from nuclear tests for isotopic analysis. It created a network of stations around the world to register the seismic effects of nuclear explosions. Most important, in 1960 it began to launch reconnaissance satellites that could take detailed photographs of nuclear sites in the Soviet Union and China. Richelson occasionally speculates about the role of communications intercepts and of spies, but these appear from his account to have been much less important than the other methods of collecting information.

Through these means the United States has gathered a vast quantity of data, sometimes to surprising effect. Intelligence played a crucial role in the cold war, for instance, by reducing uncertainty about Soviet nuclear forces. Alongside such successes, however, there have been failures. One notable example concerned the first Soviet test, which took place in August 1949, much sooner than the C.I.A. had predicted. Another was the failure to detect Indian preparations for tests in May 1998, even though at an earlier time the United States, with the help of satellite intelligence, had managed to learn about preparations the Indians were making and to head off their tests.

But the most serious failure of all was in Iraq in 2003, because in no other case did the intelligence assessments serve as justification for the use of military force. The information needed for avoiding political surprise is one thing. That needed for preventive war is quite another, if only because of the consequences of making a mistake.

Beyond making the uncontroversial recommendation that "aggressive and inventive intelligence collection and analysis" should continue, Richelson draws no general conclusions. That is a pity, because his rich material points to issues that cry out for further analysis. He suggests in one or two cases that failures sprang from the mind-set of the intelligence community, but he does not elaborate on this point. He has little to say about relations between policy makers and the intelligence community, even though the quality of intelligence and the use made of it depend heavily on that relationship.

His focus is no less narrow in his discussion of foreign nuclear projects. He concentrates on the programs themselves, paying very little attention to their political context. Does that reflect a technological bias in nuclear intelligence? Would, for example, the prewar assessment of Iraqi nuclear capabilities have been more accurate if it had paid more attention to the broader political and economic circumstances of Hussein's regime?

The task of intelligence has become more complex than it was during the cold war. A single dominant nuclear opponent has now been replaced by a number of nuclear states, along with states and stateless terrorists that are aiming to get their hands on nuclear weapons. Meanwhile, the technology needed for producing nuclear weapons has become easier to acquire.

Many critics believe the recent performance of the intelligence community shows it has not responded adequately to this new situation. Richelson does not have much to say on this question; nor does he discuss the likely impact of the current reforms, initiated in response to the Iraq war, on the quality of intelligence. His reticence may imply that he does not think reform is necessary. Still, it is disappointing that he does not draw on his historical survey to discuss whether new approaches are needed for dealing with nuclear threats, and, if so, what those new approaches might be.

The nuclear deal reached during President Bush's recent visit to India unleashed a predictable wave of criticism. From editorial and op-ed pages to Congress, led by the left but supported on the right, the administration has been assailed for making a bad bargain.

Under the agreement, which still needs congressional approval, India would open much of its nuclear facilities to international inspections in return for gaining access to the world's supplies of uranium and U.S. nuclear expertise.

The attacks on the deal reflect the view of the nonproliferation lobby -- the experts and policymakers whose central concern is to stop the spread of nuclear weapons. I share their aim. But American arguments against the India deal are misleading and only expose the deep contradictions, if not hypocrisy, of our own nuclear policies.

There are two main criticisms of the agreement: first, it undermines the Nuclear Nonproliferation Treaty, the NPT, and second, it permits, even encourages, India to expand its nuclear weapons production.

The NPT issue is particularly sensitive at a time when the international community is trying to persuade Iran to give up certain nuclear technologies which many nations fear are part of a secret bomb program.

The NPT created two sets of global rules -- one for the five nuclear weapons powers it recognizes (China, the United States, Russia, Britain and France) and another for everyone else. The five, for example, allow only "voluntary'' international safeguards on their civilian nuclear facilities. They have no obligation to open their military programs to any kind of scrutiny. And the NPT places no real limits on their arsenals, other than a vague commitment to reduce and eventually eliminate all nuclear weapons.

The rest must open their nuclear energy programs fully to international inspection and agree never to build bombs. In exchange, they gain access to the peaceful uses of nuclear energy.

Iran -- and North Korea -- made that bargain and can be held to account for breaking the rules. But India consistently regarded that as an unequal trade-off and never signed the NPT; neither did Pakistan and Israel, two other nuclear weapons states.

India's nuclear program is the product of decades of largely indigenous effort; it did not result from secretive proliferation in violation of the NPT.

The deal with India turns the five into six. It treats India as a de facto member of the inner club. The deal would require changes in U.S. law to remove existing restrictions on the transfer of nuclear energy technology, changes that would allow India to be treated no differently from China.

That does not weaken the NPT -- it strengthens it. It brings it more into accord with reality and gives India a stake in a system it had previously rejected as unfair. It paves the way for India to join the Nuclear Suppliers Group, the international organization that controls nuclear exports.

The critics are right that the deal enables India to expand its production of fissile materials to make nuclear warheads. Eight of India's 22 power reactors will remain outside international controls, along with a new breeder reactor. The Indians fought for that exemption because they feel their nuclear arsenal may not be large enough to deter a nuclear first strike by Pakistan or China in the future. Critics fear that with increased access to uranium and limited inspections, India will set off an arms race in South Asia.

Again, the agreement simply treats India like the five. Nonproliferation experts claim that unlike India, however, the five have halted their production of plutonium and highly enriched uranium that could be used to build new weapons. This is true, but misleading.

The five have massive stockpiles of fissile material built up during the Cold War. "If I've got a full pantry, it's easy for me to swear off trips to the supermarket,'' said Michael Levi, an arms-control expert at the Council on Foreign Relations.

Moreover, the United States has embarked on a new program to rebuild its nuclear weapons production capability, including creating new facilities to produce plutonium cores for warheads and to assemble them.

India has agreed to back a global pact to cut off fissile-material production. But the Bush administration does not support a treaty that would actually verify this is taking place. And the U.S. Senate has refused to ratify the Comprehensive Test Ban Treaty that would permanently halt any new testing of nuclear weapons.

A Congress that can support those policies is hardly in a position to challenge the administration's agreement with India. Rather than block the U.S.-India deal, it makes more sense to improve it. This could include reaching agreements for cooperation between the two countries to ensure the safety and security of nuclear facilities, including those for military purposes, suggested Stanford Professor Scott D. Sagan, a leading expert on nuclear safety and nonproliferation. "Reducing the risk of terrorist theft of nuclear materials or weapons in India would also help protect the United States,'' argues Sagan.

Beyond that, the six acknowledged nuclear powers should begin to seriously fulfill their part of the NPT bargain -- to cap fissile-material production, to ban nuclear testing, and to eventually radically reduce stored arsenals of nuclear weapons and materials.

SEOUL, Korea - The visit last month of North Korea's diminutive dictator Kim Jong Il to China is still making waves here in the South Korean capital.

The Chinese rolled Kim through showcases of their market reforms. The North Korean leader, who once denounced the Chinese for retreating from socialism, responded with dutiful words of praise for the Chinese model.

South Koreans applaud any evidence that Kim may be headed down a Chinese-style path. Like the Chinese, most South Koreans believe this may be the only way to ultimately persuade the North to abandon its nuclear weapons program.

But in conversations here with senior South Korean officials and others closely involved with North Korea, I detected unease, even alarm, at the growth of China's influence and presence in the North. Some talked darkly about a Chinese "takeover'' of the North.

South Korean mixed feelings about China are not new. But the Kim visit comes on top of a rapid broadening of Chinese economic ties to North Korea, described in detail in a new report issued by the International Crisis Group. Chinese trade and investment in North Korea has reached $2 billion annually. Bridges and highways in and out of North Korea are being built, making it easier to ship iron ore and other raw materials out.

Hundreds of Chinese firms are investing into North Korea, in some cases grabbing deals away from South Korean companies.

Is China willing to use this expanded influence to compel Pyongyang to give up nuclear weapons? Some in the Bush administration still cling to that hope. But the report argues strongly against that happening.

China may again drag Pyongyang back to the stalled six-party talks that it hosts. And it will move quickly to curb any North Korea provocation, such as a nuclear test, that could lead to war.

But China has an overriding interest in stability as well, opposing any attempt to destabilize the Kim government. The Chinese will cooperate to curb Pyongyang's laundering of counterfeit money through their banks, the report says, but will not shut down the North's banking operations in China.

South Koreans don't differ with China on the need to engage the North. Their own economic ties with the North are deepening. And Seoul too is consumed with the danger of triggering a war by trying to cut off the North's economic lifeline.

But South Koreans now also worry that China's deepening stake in the North will only perpetuate the division of the Korean Peninsula.

A South Korean businessman who is deeply engaged in dealings with the North argued to me privately that the North Koreans are unhappy with their dependence on Beijing and eager for an alliance with the United States. By refusing to deal directly with Kim Il Jong, he argued, "the Bush administration is pushing North Korea into the camp of China.''

We should explore such claims with a healthy dose of skepticism. The North Koreans are masters at playing the Chinese and South Koreans against each other, as they did with the Russians and Chinese during the Cold War.

More important, South Korean nervousness about China comes together with renewed interest in shoring up the strained alliance with the United States. This is partly behind a decision to negotiate a free-trade agreement (FTA) with the United States this year.

A free-trade agreement between the United States and Korea, one of the largest economies in the world, would be good for both economies. It should open more markets in Korea, removing a host of barriers such as restrictions on foreign investment. Korean officials, led by a young and ambitious American-trained trade minister, believe an FTA will spur a new round of needed internal reform and a jump in growth.

Anti-FTA protests were already taking place as I was discussing this with Korean officials. More are sure to come from those, such as farmers, most threatened by more open markets. But officials say the president and his government are committed to pushing this through.

Privately, Korean officials hope the FTA will also remind Koreans and Americans of the value of their alliance. It gives both sides something to talk about other than to dwell on their differences over North Korea. We should push hard from both sides to quickly finish an FTA deal -- and continue to talk quietly about our shared interests in maintaining a strategic balance in Northeast Asia.

What is South Korea's strategic posture in East Asia?

After the Korean War ended in 1953, South Korea and the United States established a political and security alliance that has lasted more than half a century. "For a number of decades, South Korea primarily defined itself as a U.S. ally, with the enemy to the north," says Donald Gregg, president of the Korea Society and a former U.S. ambassador to Korea. However, South Korea is now trying to create a new role for itself in Asia. Seoul is exploring a growing economic relationship with China--which passed the United States in 2003 to become South Korea's largest trading partner--and its policy of engagement and growing cooperation with North Korea is pulling it away from the United States. "All we know for sure is that South Korea's role is no longer junior partner to the U.S.," says David Kang, a visiting professor of Asian studies at Stanford University. "The days when they would just unquestioningly follow the U.S. are over."

Kang and other experts say Seoul is beginning to shift its focus towards increasing regional ties with its Asian neighbors. The U.S.-South Korea relationship, while still strong, is not as exclusive as it has been in the past. "South Korea is still an ally of the United States ... nevertheless, it has been the most active country in promoting East Asian cooperation and integration, and will probably continue to do so," says Charles Armstrong, professor of history and director of the Center for Korean Studies at Columbia University.

What are South Korea's biggest foreign policy challenges?

Dealing with North Korea while preserving its relationship with the United States, maintaining relations with Japan, and addressing potential long-term military or economic threats from China, experts say. But "the major issue for Seoul is overwhelmingly North Korea, and everything else gets filtered through that lens," Kang says. South Korea looks to its northern neighbor with the goal of eventual reunification, and therefore seeks economic cooperation and political engagement to smooth relations and slowly move down that path. The United States, on the other hand, is primarily seeking to prevent North Korea from gaining nuclear weapons, and has refused to engage with Pyongyang until that issue is resolved.

Other experts see a disconnect between how South Korea views its role in the region and how other nations see it. South Korean officials talk of playing a "balancing" or mediating role in regional disputes, including tensions between China and Japan and the nuclear standoff between the United States and North Korea. But South Korea's "actual ability to mediate and balance is limited," says Armstrong. And while South Korean President Roh Moo-Hyun has expressed hopes of building Seoul into a logistics and business hub for the region, existing tensions on the peninsula--including international fears that North Korea is amassing a nuclear arsenal--cloud any long-term economic plans. As things stand, South Korea has the world's 11th largest economy, but not a corresponding level of political clout.

How is South Korea dealing with North Korea?

Through a policy of active engagement. In 1998, Former President Kim Dae-Jung introduced the "Sunshine Policy" aimed at improving ties with North Korea while assuring Pyongyang that Seoul is not trying to absorb it. Since then, "the degree of economic interaction between south and north has substantially increased," Armstrong says. Kim and North Korean President Kim Jung-Il met at a historic summit in 2000, and increasing progress has been made on a range of issues, from economic--increased rail links and joint projects like the Gaesung industrial complex--to social and symbolic, including cross-border family visits and Korean athletes marching together under a single flag at the Olympics. Trade between the two countries reached $697 million in 2004, and South Korea is now Pyongyang's second-largest trading partner after China.

South Korea sees engagement with North Korea as yielding far more benefits than confrontation. "South Korea is reorienting itself toward reconciliation and eventual reunification of the peninsula," Gregg says. South Korean officials say reunification would reduce the burden on each side of maintaining huge armies, help improve living standards, draw international investment, create employment, and help avert the worst possibility: open war on the Korean peninsula.

What is South Korea's relationship with China?

South Korea is developing increasingly warm relations with its giant western neighbor. "There is a real fascination with China in South Korea, and the flow of investment, exports, students, tourists, and businessmen going to China from South Korea has exploded in the last several years," Armstrong says. Bilateral trade between Seoul and Beijing reached $90 billion in 2004, a 42 percent increase from 2003. The two countries also agree politically on issues ranging from opposition to Japanese Prime Minister Junichiro Koizumi's visits to the Yasukuni war shrine, to accord on how to deal with North Korea's nuclear ambitions. China is also choosing the path of engagement with North Korea, and helping Pyongyang find a "Chinese way" to develop: that is, increasing economic openness without sacrificing political control. "On the whole, [South Korea and China] see pretty much eye to eye on the major geopolitical issues," Kang says.

Beijing, like Seoul, is investing in North Korea, which has ample natural resources--including coal, iron, and gold--and a low-cost labor force. In 2003, Chinese investment in North Korea was $1.1 million; in 2004, it ballooned to $50 million; and in 2005, it was expected to reach $85-90 million. The volume of trade between China and North Korea reached $1.5 billion in 2005, making Beijing Pyongyang's largest foreign trading partner. North Korean leader Kim Jung-Il, who rarely travels, emphasized Beijing's importance to his country by visiting China in January.

South Korea is positioning itself to be closer to an ascendant China, but trying to do it without jeopardizing existing ties with the United States. South Korea's biggest worry, experts say, is being pulled into a conflict between the United States and China over Taiwan.

What's the relationship like between South Korea and Japan?

"Very bad at the moment in terms of public diplomacy and popular opinion," Columbia University's Armstrong says. South Korean wariness of Japan dates back at least to 1910, when imperial Japan invaded Korea and ruled it as a colony for thirty-five years. During the occupation, Japanese efforts to suppress Korean language and culture earned Korean enmity. During World War II, the Japanese practice of using "comfort women"--women from occupied countries, mostly Korea, who were forced to serve as prostitutes for the Japanese army--increased the anti-Japanese feeling.

South Koreans, and others across the region, are also infuriated by Koizumi's annual visit to the Yasukuni shrine. The site honors more than two million Japanese war dead, but includes the remains of more than a dozen convicted war criminals. South Korea also has disputes with Japan over territory. Both countries claim a group of islands--and the fishing and mineral rights around them--in the Sea of Japan that the Koreans call Dokdo and the Japanese call Takeshima. And many critics in South Korea and across Asia accuse Japan of whitewashing its wartime atrocities in its grade-school textbooks.

But much of the South Korean conflict with Japan may be for domestic political consumption, some experts say. "Under the surface, I would say the degree of interaction [between Seoul and Tokyo] remains high and, in the economic realm, is rather good," Armstrong says.

How is South Korea dealing with the United States?

While experts say most South Koreans still consider the U.S.-Korean alliance the backbone of their security relationship, time has passed and attitudes are shifting. A new generation of South Koreans, assertive and nationalistic, are less mindful of the Korean War--and less grateful for American intervention in the conflict that left nearly three million Koreans dead or wounded--and more resistant to what they see as a U.S. attempt to impose its values and Washington's singular focus on terrorism. The United States has opposed South Korean engagement efforts with North Korea, and has also moved to increase its ties with Japan. The Bush administration's foreign policy, including the war on terror, its punitive stance toward North Korean nuclear weapons, and particularly the invasion of Iraq, is highly unpopular in South Korea, according to opinion surveys there.

South Koreans are also increasingly demanding more control over their country's military and political affairs. In 2004, the United States returned several military bases to Korean control, and agreed to withdraw 12,500 of the 37,500 U.S. troops currently stationed in Korea by 2008. U.S. officials, including Defense Secretary Donald Rumsfeld, had been pushing for South Korea to take more of a role in the defense of the Korean peninsula, to free up U.S. forces for deployment elsewhere. But, all differences aside, Seoul is still eager to cooperate with the United States. South Korea, with some 3,000 troops in Iraq, is the third-largest member of the U.S.-led coalition there, behind the United States and Britain.

What is the recent history of the region?

Poised between China and Japan, fought over by the United States and Russia, the Korean peninsula long has played a central role in Asia's geopolitical affairs. After World War II, Japanese colonial rule gave way to U.S. and Soviet trusteeship over the southern and northern halves of Korea, respectively. The peninsula was divided at the 38th Parallel. In 1948, the southern Republic of Korea and the northern Democratic People's Republic of Korea, under Kim Il-Sung, were established.

In 1950, North Korean forces invaded South Korea, starting a conflict that brought in China on the North Korean side and a U.S.-led UN coalition on the South Korean side. While an armistice was agreed to in 1953, a formal peace treaty was never signed. In 1954, the United States agreed to help South Korea defend itself against external aggression in a mutual defense treaty. U.S. troops have been stationed in Korea since then. In addition to this important security relationship, shared interests in the last fifty years have included fighting communism and, since the 1980s, establishing a strong democracy and fostering economic development. However, in recent years strain has emerged on a range of issues, none more important than how to handle Pyongyang.