"Blocking research activities is similar to blocking the light" was the poetic phrase used by Iran's head of nuclear research, Hossein Ghafourian, on Iranian radio last weekend to defend Iran's plans to restart their nuclear centrifuge research.

 It is precisely the fear of such blinding and incinerating nuclear light that is moving the world's diplomats to speak out with increasing stridency and urgency in the face of Iran's intent to recommence nuclear research and testing that might lead to their development of nuclear weapons.

 German Foreign Minister Frank-Walter Steinmeir responded to Iranian words of intent to break the seals and restart the nuclear program: "This marks a breach of Tehran's commitments. [Iran is sending] very, very disastrous signals. It cannot remain without consequences ... We have had two very, very grave signals from the Iranian government over the past weekend."

 French Foreign Minister Philippe Douste-Blazy warned: "We urge Iran to immediately and unconditionally reverse its decision ... [It] is a reason for very serious concern." European Foreign Minister Javier Solana warned that the situation is "serious." Mohammed El Baradei, the head of the International Atomic Energy Agency (IAEA) said he is "losing his patience" with Iran and that they were approaching "a red line for the international community."

 These statements follow actions last Saturday by all five permanent members of the U.N. Security Council (China, Russia, France, Britain and the United States). Each country separately sent a demarche (a formal diplomatic communique) to Iran warning the country it could face United Nations Security Council censure and sanctions.

 When cautious and circumspect European diplomats use words like "serious," "grave," "disastrous," "red line for international community," "urge Iran to immediately and unconditionally reverse its decision," the rest of us should take these phrases as unambiguous evidence that an international crisis of the first water is fast building.

 The event that may precipitate formal diplomatic action will occur in March, when IAEA head El Baradei will file his next report to the U.N. on the nuclear program status of Iran.

 The question remains whether all this diplomatic agitation will lead to effective international action. It is generally recognized among leading American and European statesmen that the period of negotiating with Iran is almost at an end. We are now entering a period of what is being called coercive diplomacy. But what kind of coercion is being contemplated? And what are the calculations that are going into selecting the means of coercion?

 As Dr. Henry Kissinger once wrote, the advantage that historians have over statesmen is that historians know all the facts and have years to assess them. Statesmen must act without knowing all the facts and without having enough time. 

 The spectrum of actions range from mere criticism, to censure, to diplomatic isolation, to economic sanctions as punishment, to specific barring of importation into Iran of products and services critical to nuclear weapons production, to military actions intended to physically destroy Iran's nuclear capacity.

 All the possible actions short of the ultimate military one rely on assumptions that are not fully verifiable. Diplomatic isolation assumes the Iranian regime places a high value on non-isolation.

  Economic sanctions assume that they can have their desired coercive effect before Iran can develop nuclear weapons. And denying Iran products and services needed to develop nuclear weapons assumes that they are and will remain unable to develop nuclear weapons exclusively from what they possess internally (and that such a ban on such imports could be enforced effectively even regarding such countries as Russia, China, North Korea and Pakistan, as well as the international black market.)

 Nobody asserts (not even high U.S. government officials) that our intelligence within Iran is sufficient to certify Iran's domestic capacities.  But there appears to be a high level of belief in our government that Iran needs some outside help to fully develop and manufacture a nuclear weapon.

 If that assumption is right, and if we and other leading countries under the auspices of the United Nations (or otherwise) can enforce such an embargo without damaging leakage, then the sanctions and embargo as a coercive device would be a sufficient protection for the world.

 Every action has its risks and costs. Prompt American military action unsanctioned by the U.N. would have very high diplomatic, geopolitical, world image and domestic partisan division costs, but would assure a non-nuclear Iran for a period of years.

 Relying on embargo and sanction comes cheap -- if it works. But as we can't know Iran's full internal capacity, the likelihood of a leak-free embargo, nor the will of the Iranian regime, the contingent price we would pay for failure would be a fait accompli nuclear Iran. Also, this plan relies on Israel forbearing from taking its own military action -- which they might or might not take, and which might or might not be effective.

 From all available evidence, it appears that international embargo of critical nuclear elements, combined with diplomatic isolation and more general economic sanctions, are likely to form the substance of the American and international response if Iran does not agree to stand down voluntarily in the next month or so.

 Any action is a calculated risk. We shall see whether today's statesmen are making the right calculations.