This week President Bush will seek to focus the nation's attention on border security and immigration reform. But the president's proposals won't protect Americans from our gravest cross-border threat: the possibility that a ship, truck or train will one day import a 40-foot cargo container in which terrorists have hidden a dirty bomb or nuclear weapon.

The Bush administration maintains that it has a smart strategy to reduce this risk. A new 24-Hour Rule requires that importers report the contents of their containers to customs inspectors one day before the boxes are loaded on ships bound for the United States. The Department of Homeland Security's National Targeting Center then reviews the data, checking against other intelligence to determine which boxes may pose a threat. Although the containers deemed high risk are inspected at cooperating foreign ports or when they enter the United States, the rest--more than 90 percent--land here without any perusal.

We have two concerns about this strategy. First, it presumes that the United States government has good enough intelligence about Al Qaeda to reliably discern which containers are suspicious and which are not. But our inability to thwart the attacks in Iraq demonstrates that we lack such specific tactical intelligence. And supporting customs inspectors, who must make the first assessment of risk, is not a priority for the intelligence agencies. Inspectors must rely on their experience in spotting anomalies--a company that claims to be exporting pineapples from Iceland, for example.

Second, determined terrorists can easily take advantage of the knowledge that customs inspectors routinely designate certain shipments as low risk. A container frequently makes 10 or more stops between its factory of origin and the vessel carrying it to American shores. Many of the way stations are in poorly policed parts of the world. Because name-brand companies like Wal-Mart and General Motors are widely known to be considered low-risk, terrorists need only to stake out their shipment routes and exploit the weakest points to introduce a weapon of mass destruction. A terrorist cell posing as a legal shipping company for more than two years, or a terrorist truck driver hauling goods from a well-known shipper, can also be confident of being perceived as low risk.

So what needs to be done? A pilot project under way in Hong Kong, the world's largest container port along with Singapore, offers one piece of a potential solution. At an estimated cost of $7 per container, new technology can photograph the box's exterior, screen for radioactive material, and collect a gamma-ray image of a box's contents while the truck on which it is carried moves at 10 miles per hour.

Terrorists can defeat radiation sensors by shielding a dirty bomb with dense materials like lead. But by combining those sensors with gamma ray images, the Hong Kong system allows inspectors to sound the alarm on suspiciously dense objects. Inspectors would need to analyze enough of the scans--perhaps 20 percent to 30 percent--to convince terrorists that there is a good chance that an indistinct image will lead a container's contents to be sent for more reliable X-ray or manual examinations. Images of container contents would then be reviewed remotely by inspectors inside the United States who are trained to spot possible nuclear weapons.

If terrorists were to succeed in shipping a dirty bomb, for example, the database of these images could serve as a kind of black box--an invaluable forensic tool in the effort to identify how and where security was breached. That information could help prevent politicians from reacting spasmodically and freezing the entire container system after an attack.

Such a program could significantly reduce the likelihood that terrorists will smuggle plutonium or a dirty bomb through American ports. But it still would not stop a terrorist from importing highly enriched uranium, which can be used to construct a nuclear weapon. Lengthening the time that a container is screened for radiation would help, and this could be done without increasing waiting times if additional monitors were added to the Hong Kong system near the gate where the trucks must already stop for driver identification checks. Better still would be for the Department of Homeland Security to make the development of new technology that can recognize the unique signature of highly enriched uranium an urgent priority.

Finally, we must find ways to ensure that terrorists do not breach containers before shipments arrive at loading ports. Sensors should be installed inside containers in order to track their movements, detect any infiltration and discern the presence of radioactive material. Where boxes are loaded, certified independent inspectors should verify that companies have followed adequate protocols to ensure that legitimate and authorized goods are being shipped.

Taken together, these recommendations will require new investments and an extraordinary degree of international cooperation. But increased container security will not only help the United States prevent terrorism, it will also help all countries reduce theft, stop the smuggling of drugs and humans, crack down on tariff evasion and improve export controls. What's more, such a program would require an investment of just one one-hundredth of the capital that could be lost if we shut down the global container shipping system after an attack.

Container security is a complex problem with enormous stakes. American officials insist that existing programs have matters well in hand. But we cannot afford to take these perky reassurances at face value while the same officials fail to embrace promising initiatives like the Hong Kong pilot project.

In the old popular song about the rout by Americans at New Orleans during the War of 1812, the British "ran so fast the hounds couldn't catch 'em." Even allowing for patriotic hyperbole, it can hardly be argued that the British extricated themselves with a great deal of dignity, particularly given that another battle in the same war inspired the American national anthem.

The impact of that defeat on the British national psyche is now obscure, but nearly two centuries later, as the Americans and their British allies seek to extricate themselves from Iraq, the story of how a superpower looks for a dignified way out of a messy and often unpopular foreign conflict has become a historical genre of sorts. As the pressure to leave Iraq increases, that genre is receiving new and urgent attention.

And in the shadow of the bleak and often horrific news emerging from Iraq nearly every day, historians and political experts are finding at least a wan hope in those imperfect historical analogies. Even in the absence of a sudden and dramatic shift on the battlefield toward a definitive victory, there may still be a slight opening, as narrow as the eye of a needle, for the United States to slip through and leave Iraq in the near future in a way that will not be remembered as a national embarrassment.

Most of the recent parallels do not seem to offer much encouragement for a confounded superpower that wants to save face as it cuts its losses and returns home. Among them are the wrenching French pullout from Algeria, the ill-fated French and American adventures in Vietnam, the Soviet humiliation in Afghanistan and the disastrous American interventions in Beirut and Somalia.

Still, there are a few stories of inconclusive wars that left the United States in a more dignified position, including the continuing American presence in South Korea and the NATO peacekeeping mission in Bosnia. But even those stand in stark contrast to the happier legacy of total victory during World War II.

The highly qualified optimism of these experts about what may still happen in Iraq - let's call it something just this side of hopelessness - has been born of many factors, including greatly reduced expectations of what might constitute not-defeat there. The United States already appears willing to settle - as if it were in a relationship that had gone sour but cannot quite be resolved by a walk out the door, punctuated with a satisfying slam.

Alongside the dampening of hopes, there has also been a fair amount of historical revisionism regarding the darker tales of conflicts past: a considered sense that if the superpowers had made different decisions, things could have turned out more palatably, and that they still might in Iraq.

Maybe not surprisingly, Vietnam is the focus of some of the most interesting revisionism, including some of it immediately relevant to Iraq, where the intensive effort to train Iraqi security forces to defend their own country closely mirrors the "Vietnamization" program in South Vietnam. If Congress had not voted to kill the financing for South Vietnam and its armed forces in 1975, argues Melvin R. Laird in a heavily read article in the current issue of Foreign Affairs, Saigon might never have fallen.

"Congress snatched defeat from the jaws of victory by cutting off funding for our ally in 1975," wrote Mr. Laird, who was President Nixon's defense secretary from 1969 to 1973, when the United States pulled its hundreds of thousands of troops out of Vietnam.

In an interview, Mr. Laird conceded that the American departure from Vietnam was not a pretty sight. "Hell, the pictures of them getting in those helicopters were not good pictures," he said, referring to the chaotic evacuation of the American embassy two years after Vietnamization was complete, and a year after Nixon resigned. But on the basis of his what-if about Vietnam, Mr. Laird does not believe that all is lost in Iraq.

"There is a dignified way out, and I think that's the Iraqization of the forces over there," Mr. Laird said, "and I think we're on the right track on that."

Many analysts have disputed the core of that contention, saying that large swaths of the Iraqi security forces are so inept they may never be capable of defending their country against the insurgents without the American military backing them up. But Mr. Laird is not alone in his revisionist take and its potential application to Iraq.

William Stueck, a history professor at the University of Georgia who has written several books on Korea, calls himself a liberal but says he buys Mr. Laird's basic analysis of what went wrong with Vietnamization.

Korea reveals how easy it is to dismiss the effectiveness of local security forces prematurely, Mr. Stueck said. In 1951, Gen. Matthew Ridgeway felt deep frustration when Chinese offensives broke through parts of the line defended by poorly led South Korean troops.

But by the summer of 1952, with intensive training, the South Koreans were fighting more effectively, Mr. Stueck said. "Now, they needed backup" by Americans, he said. By 1972, he said, South Korean troops were responsible for 70 percent of the front line.

Of course, there are enormous differences between Iraq and Korea. Korean society was not riven by troublesome factions, as Iraq's is, and the United States was defending an existing government rather than trying to create one from scratch.

Another intriguing if imperfect lesson can be found in Algeria, said Matthew Connelly, a Columbia University historian. There, by March 1962, the French had pulled out after 130 years of occupation.

That long colonial occupation, and the million European settlers who lived there before the bloody exodus, are major differences with Iraq, Mr. Connelly noted. But there were also striking parallels: the insurgency, which styled its cause as an international jihad, broke down in civil war once the French pulled out; the French, for their part, said theirs was a fight to protect Western civilization against radical Islam.

Like President Bush in Iraq, President Charles de Gaulle probably thought he could settle Algeria in his favor by military means, Dr. Connelly said. In the short run, that turned out to be a grave miscalculation, as the occupation crumbled under the insurgency's viciousness.

Over the long run, though, history treated de Gaulle kindly for reversing course and agreeing to withdraw, Mr. Connelly said. "De Gaulle loses the war but he wins in the realm of history: he gave Algeria its independence," he said. "How you frame defeat, that can sometimes give you a victory."

The Americans in Beirut and the Soviets in Afghanistan are seen, even in the long view, as cases of superpowers paying the price of blundering into a political and social morass they did not understand.

For the Soviets, that mistake was compounded when America outfitted Afghan rebels with Stinger missiles capable of taking down helicopters, nullifying a key Soviet military superiority. "I don't think they had a fig leaf of any kind," said Henry Rowen, a fellow at the Institute for International Studies at Stanford who was assistant secretary of defense for international security affairs from 1989 to 1991. "They just left."

In Beirut, the Americans entered to protect what they considered a legitimate Christian-led government and ended up, much as in Iraq, in the middle of a multipronged civil conflict. In October 1983, a suicide attack killed 241 American servicemen at a Marines barracks, and four months after that, with Muslim militias advancing, President Ronald Reagan ordered the remaining marines withdrawn to ships off the coast, simply saying their mission had changed. The episode has been cited by Vice President Dick Cheney as an example of a withdrawal that encouraged Arab militants to think the United States is weak.

Today, even as expectations for Iraq keep slipping, some measure of victory can still be declared even in a less-than-perfect outcome, said Richard Betts, director of the Saltzman Institute of War and Peace Studies at Columbia. For example, he said, an Iraqi government that is authoritarian but not totalitarian might have to do.

The key point, he said, is that under those circumstances, the outcome "doesn't look like a disaster even if it doesn't look good."

United Nations Secretary-General Kofi Annan created the High-Level Panel on Threats, Challenges, and Change in September 2003 with SIIS and CISAC senior fellow Stephen J. Stedman as its research director to identify the major global threats and generate new ideas about policies and institutions to enable the U.N. to be effective in the 21st century.

The panel issued a four-part report, A More Secure World: Our Shared Responsibility, in December 2004.

PART ONE: The panel identifies six types of threats of greatest global concern: war between states; violence within states; poverty, infectious disease, and environmental degradation; nuclear, chemical, biological, and radiological weapons; terrorism; and transnational crime. A collective security system must take all member states' threats seriously and deal with them equitably.

PART TWO: In prescribing policies to prevent threats from spreading or worsening, the report emphasizes development as the first line of defense. Combating poverty and infectious disease, the panel argues, will save millions of lives and strengthen states' capacity to deter terrorism, crime, and proliferation of nuclear and biological weapons. The report also urges the U.N. to improve its capacity for preventive diplomacy and mediation and to forge a counterterrorism strategy.

PART THREE: The report reiterates the U.N.'s recognition of states' right to self-defense, but also suggests that the Security Council should consider stepping in more often to exercise its preventive authority. Peacekeeping, peace enforcement, and peace building are vital to global security, and developed nations should do more to transform their armies into units suitable for peace operations. Post-conflict peace building should be a core function of the U.N.

PART FOUR: The report prescribes revitalization of the Security Council and the General Assembly, and creation of a new Peacebuilding Commission. On the Security Council, the report provides two options for achieving reforms: one would appoint new permanent members, and the other would establish new long-term, renewable seats. Neither option creates any new vetoes.