Iran has said, "No, for now," to the U.N. Security Council's legally binding demand that Tehran suspend enrichment of uranium, as a first step toward resuming negotiations over the future course of its nuclear-energy program and broader relations with the West. Iran's militant leaders are inspired by Hezbollah's gritty fight with the vaunted Israeli army and the U.S. debacle in Iraq. They are emboldened by the sense that Security Council states have enforcement fatigue -- an unwillingness to confront tough guys who ignore international demands.

It's now time for the U.S. to quietly rally defense and foreign ministries in Europe, the Middle East and Asia to develop operational plans for containing and deterring a nuclear-armed Iran. Far from throwing in the towel or abandoning diplomacy in favor of warfare, devising a deterrence and containment strategy now would allay international fears that Washington uses U.N. diplomacy as a prelude to military-delivered regime change. Building international capabilities to contain a nuclear-armed Iran would have the double benefit of putting muscle into the Security Council's effort to dissuade Iran from acquiring nuclear weapons capability in the first place.

The first step is to convince Iran's leaders that their sovereignty and security will not be threatened if they desist from supporting or conducting violence outside their borders. Iran's leaders -- odious or not -- must know that they do not need nuclear weapons or proxy war for their survival; the regime's survival is best guaranteed by not fighting. The incentive package that France, Germany, the U.K., the U.S., Russia and China have recently offered to negotiate contains most of what is necessary to show Iran it will live better without producing fissile materials. What it lacks is a clear U.S. commitment to live with the government in Tehran, even as we compete with it politically and morally.

If Washington will forswear regime change and the Iranian government still refuses to negotiate terms for conducting an exclusively civilian nuclear program, then Tehran must be convinced it will suffer greatly for threatening its neighbors and Israel, directly or by proxy. The message must be: "The United States and other major powers will work more closely than ever with your neighbors to monitor your activities and establish capabilities to respond forcefully and immediately to any scale of terrorism, subversion or war that you visit on others. If you have nuclear weapons, we won't tolerate your export of violence."

The practical threat from Tehran is an extension of what just happened in Lebanon. With nuclear weapons, Iranian Revolutionary Guards and other militant actors would supply more and better weapons to Hezbollah, Islamic Jihad and Hamas, and stimulate their campaigns against Israeli and American targets, confident that their nuclear weapons would deter major counterattacks against Iran. Iran's collective leadership -- and the Persian nation -- did not grow old by being suicidal. President Mahmoud Ahmadinejad is young and zealous, but not completely in charge. Tehran will test the limits of subversion, low-intensity conflict and terrorism, while seeking to avoid a nuclear war with the U.S. or Israel.

Iran's neighbors will be torn between accommodating Tehran's rising power and seeking greater U.S. security cooperation. As during the Lebanon war, Arab governments will not want to provoke Tehran and their own anti-American populations. At the same time, these governments dread the arrogance and subversion they expect from a regionally dominant Iran. The present moment when Iran's nuclear capabilities remain in doubt must be seized to discreetly develop cooperative strategies to contain Tehran's capacity to project power and influence.

This would be easier if Hezbollah were disarmed, and Iranians less emboldened by their military capabilities. Short of that, if Damascus can be induced to stop facilitating Hezbollah's arms supply and training, Iranians will begin to see containment's potential. Washington should explore directly what it would take to induce Syria's cooperation.

Improved cooperation in intelligence-gathering and monitoring of Iranian activities must be a priority. The U.S. and Iran's neighbors should create a surveillance system to monitor all Iranian aircraft movement and potential missile launches. This is needed to clarify when Iran is conducting or supporting aggression outside its borders, and to identify perpetrators and relevant targets for retaliation, which would best be done covertly. Iran's arming of Hezbollah exemplifies activities that must be nipped in the bud, by covert force if necessary.

Iranian officials today bristle at U.S. intelligence-gathering and networking around their borders and among their restive minority communities. They denounce these activities as signs of a U.S. regime-change strategy that, implicitly, justifies Iran's need of nuclear-weapon capability. The U.S. must clarify that as long as Tehran is acting aggressively and seeks or possesses nuclear weapons, the international community has no choice but to gather intelligence vigorously. Similarly, as long as Tehran is developing ballistic missiles configured to carry nuclear weapons, the U.S. and Iran's neighbors are justified in deploying theater ballistic missile defenses. Again, cooperation in deploying such defenses should be as secret as possible to reduce political controversy. A nuclear-armed Iran that advocates wiping another country off the map would leave the U.S. little choice but to destroy Iranian missiles on the ground if Iran ever threatens to enter conflicts involving U.S. friends.

Mandatory international sanctions on investment, arms sales and nuclear cooperation in Iran would greatly augment containment. Such sanctions are possible only under U.N. Security Council authorization. Moscow now blocks sanctions to prevent Tehran from producing materials that could be used in nuclear weapons, and President Vladimir Putin has equivocated about stopping Iranian enrichment of uranium. But Mr. Putin has unequivocally said Iran must not acquire nuclear weapons. The West needs to find his price for clarifying that Moscow will support severe penalties if Iran proceeds to acquire nuclear weapons. This will be easier to do now than after the fact.

The U.S. and its partners should now urge the U.N. Security Council to specify that any state violating Security Council Resolution 1540's prohibition on transferring nuclear weapons to terrorists will be deemed a threat to international peace and security under Chapter VII of the U.N. Charter, which would provide authority for military reprisals. In light of Iran's ongoing defiance of Security Council demands regarding its nuclear activities, there is no justifiable excuse not to send such a warning to Tehran and others in case they break their treaty obligations not to acquire nuclear weapons.

Iranian leaders wish to perpetuate their rule, not sacrifice it. Since their illicit nuclear activities were discovered in 2002, they have acted cautiously when the major powers stood resolutely together. When resistance has been weak, Tehran has acted aggressively. It is not too early to build a framework for deterring Tehran from acting outside its borders.

Mr. Perkovich is vice president and director of the Nuclear Nonproliferation Program at the Carnegie Endowment for International Peace.

Reprinted from The Wall Street Journal © (2006) Dow Jones & Company.  All rights reserved.