Finally, we are told, there is a breakthrough in the Iranian nuclear crisis: The Bush administration and its European allies have persuaded Russia and China to vote, at the International Atomic Energy Agency meeting on Thursday, to send Iran's nuclear violations to the UN Security Council.

Allow us to point out the gray lining in the silver cloud.

Although the agency is now likely to report Iran to the Security Council, America and the Europeans agreed that the United Nations will wait at least a month before deciding on any punishment. There is little doubt what this cooling-off period is intended for: further negotiations on a proposal that would have Iran shift its large-scale, energy-related uranium enrichment work to Russia.

The Americans, British, French, Germans and Chinese have all shown support for the Russian proposal. Iran, however, showed little interest before mid-January, when it became clear the West was intent on getting tough.

Last Wednesday, Iran's chief nuclear negotiator called the Russian suggestion "positive" and predicted that it could be "perfected" through further talks. While this may seem hopeful, the Russian deal actually poses more problems than it solves.

First, even if Russia took over Iran's nuclear energy work, the religious radicals in Tehran would be left with a huge amount of dangerous equipment. The deal covers only the commercial-scale enrichment program Iran has planned for its plant at Natanz.

But Iran also has a string of shops for manufacturing centrifuges which can be used to enrich uranium to weapon grade a large inventory of centrifuge parts, a stockpile of uranium gas needed to feed the centrifuges (plus a factory to produce more), and a pilot- scale enrichment plant under construction.

Second, Iran draws a distinction between the energy-related work that would go to Russia and other enrichment activity that it likes to call "research." When Iran broke the international seals at three enrichment sites last month and resumed work, its Foreign Ministry said the move was done only for scientific interests and had nothing to do with weapons.

Even with a Russian deal, Iran is likely to insist on its right to continue such research, which would allow its scientists to develop the skills necessary to process uranium for bombs.

Last, the proposal, if accepted, would shatter the coalition of states that is finally working together to restrain Iran. Russia would certainly end its tepid support for Security Council action and would agree to let the Iranians continue their "research."

The United States is equally certain to refuse such a concession. The Europeans would be torn between the desire to see a successful end to their years of diplomatic effort and their belief that Iran's nuclear ambitions would not be adequately contained.

If we are going to negotiate with Iran, we must hold out for a solution like the one Libya accepted in 2003. Libya allowed everything useful for enriching uranium to be boxed up and carted out of the country.

It also answered all questions about its nuclear past and it revealed the names of its shady suppliers, allowing the West to counter the nuclear smuggling network run by the Pakistani scientist A.Q. Khan. Only greater pressure from the Security Council is likely to force Iran to accept a similar agreement.

The Russian proposal is a red herring aimed at helping Iran, a major trading partner of Moscow's, get out of harm's way at the very moment when the world is uniting against it. A Security Council referral came into play only because of Iran's recent behavior: the inflammatory anti-Israel statements of its president, Mahmoud Ahmadinejad, and its ill-timed decision to resume nuclear work.

If Iran snaps up the Russian offer, our last, best chance to pressure Iran in the Security Council may be lost.

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Valerie Lincy and Gary Milhollin are, respectively, a research associate and the director of the Wisconsin Project on Nuclear Arms Control.