We've been down this road before: A crisis threatens global security, and the international community is not coming together to deal with it. Hawks in the U.S. administration see the Europeans as too timid to use force and reliant on diplomacy to a fault, while many Europeans see the United States as trigger-happy and too impatient with negotiated settlements. This lack of cohesion damaged the legitimacy of the American-led war in Iraq and left U.S.-European relations in tatters. A similar disunity jeopardizes current attempts to manage Iran's nuclear aspirations, even though both sides agree that the threat posed by a nuclear Iran is grave and real.

Departing Deputy Secretary of State Richard L. Armitage positively spun the divergent U.S. and European approaches to Iran: "The [diplomatic] incentives of the Europeans," he said, "only work against the backdrop of the United States being strong and firm on this issue. In the vernacular, it's kind of a good cop/bad cop arrangement. If it works, we'll all have been successful." The problem with Armitage's hopeful outlook is that the good cop/bad cop strategy works only if pursued consciously and in coordination, and the U.S. and European approaches do not reflect that yet. In fact, they seem headed in opposite directions.

The good cops--Britain, France and Germany--recently persuaded Iran to suspend all uranium enrichment-related activities until they reach a final accord. If the mullahs cooperate, they will receive numerous economic carrots, including possible membership in the World Trade Organization (the U.S. would have to agree) and improved trade relations.

In October 2003, when the International Atomic Energy Agency was prepared to take its negative report on Iran's nuclear program to the U.N. Security Council, the mullahs cut a similar deal with the Europeans, promising to suspend all enrichment-related activities. But Iran soon grew impatient with the agreement and resumed efforts to produce the gas that feeds uranium enrichment. It similarly rushed to make as much of that gas as possible before the latest accord's deadline, undercutting confidence in the deal on both sides of the Atlantic. In another bad-faith move, Iran announced last week that it wanted to keep operating uranium-enrichment equipment for research purposes, backing off its pledge to freeze all such activities.

Enter the bad cop--the United States. It has pushed to refer the question of Iran's nuclear aspirations to the Security Council. When Secretary of State Colin L. Powell steps down, the hawkish voices in his department will probably intensify and gain influence, especially if the mullahs break the newest deal.

Armitage might be right that the discordant U.S.-European approaches will push the mullahs to hold to the deal. But the U.S. will be uncomfortable with an agreement that does not insist on any means of enforcement or verification, as is the case with the latest accord.

Iran knows that the war in Iraq colors U.S. conduct toward it. The worse Iraq gets, the less Iran worries--and the mullahs don't seem too worried at the moment. But if they break the accord with the Europeans and the Europeans respond timidly and U.S. resources are freed up as a result of an improving situation in Iraq, the U.S. could take on Iran alone--to everyone's detriment. To avoid this risk, the U.S. and Europe need to harmonize their approaches and develop a coordinated strategy for Iran. The best way to accomplish this is to agree in advance on the consequences Iran will face if it violates its commitments. For example, if the mullahs renege on the latest deal, frustrate the monitoring and verification efforts of IAEA inspectors or fail to ratify an addition to the Nuclear Non-Proliferation Treaty that allows for more invasive inspections, the U.S. and Europe should go to the Security Council, impose economic sanctions or, in the worst case, take military action.

Fortunately, diplomatic disunity over Iran does not run as deep as it did over Iraq, where even the nature of the threat was a bone of contention. Both the U.S. and Europe are worried about a nuclear Iran, and they feel strongly about enforcing the rules of nonproliferation. In June 2003, European foreign ministers required only 45 minutes to approve a document that endorsed U.N.-sanctioned use of force as a last resort against proliferators, as well as "political and diplomatic preventative measures."

If the Europeans agree to leave all responses on the table and to act decisively at the first sign of Iranian mischief, the United States would be foolish not to form a partnership with them. (It's also important that the U.S. set a better example as a member of the nonproliferation community by abandoning plans to build new mini-nuclear weapons and ratifying the Comprehensive Test Ban Treaty.)

The role the U.S. forges for itself in dealing with Iran will have significance beyond reinvesting in international order or responding to the mullahs' nuclear ambitions. Iran's despotic regime will collapse some day, and there will be a "morning after" similar to that in Iraq, where reconstruction efforts have floundered because U.S. planners underestimated the challenge of nation-building and the need for international support to make it work. When Iran makes its move toward a better government, the U.S. should be in a position to lead a coherent, collective international effort to help it get off the ground.

Yet since the severing of U.S.-Iranian ties in 1980, the U.S. has been slack in developing a viable Iran policy. Iran's nuclear ambition should be motive enough to reverse this inattention. U.S. policy toward Iran must cease to be reactive, as it is now.

In addition to working with the Europeans to curb the mullahs' nuclear efforts, the U.S. should begin crafting a strategy to work toward--and then with--a democratic Iran. Supporting a government that complies with its international obligations is certainly preferable to containing one that thwarts them. By getting involved now, the U.S. can do much to show Iranians that it will be a friend to a free Iran. A democratic Iran may still want a nuclear bomb as a matter of national pride. But a less threatening, pro-diplomacy U.S. would be in a stronger position to argue the benefits of membership in the nonproliferation community rather than life as a rogue power.

Participating in a multilateral approach to Iran's nuclear program is a great place to start. In doing so, the U.S. will signal to Iranians that its aggressive position does not reflect a desire to remake Iran in its own image but rather a desire to achieve, alongside Europe, a substantial victory for nonproliferation and international security.