FOR THE SECOND time in a year, European foreign ministers are close to striking an interim deal with Iran over its nuclear program. And once again, the United States -- whose own objective of referring Iran to the U.N. Security Council would be blocked by the accord -- is watching ineffectually from the sidelines. Here are reflected two principal failings of the Bush administration's first term. One is the weakness of its policy toward Iran, which has progressed steadily toward acquiring nuclear weapons during the past four years. The other is its inability to work with major European allies such as France and Germany, which, along with Britain, have been negotiating with Iran. Whether or not it materializes in the coming days, the new deal ought to catalyze a fresh start by President Bush on both those fronts.

The first and most urgent step is for Mr. Bush to end four years of feuding among his advisers and decide on a strategy. Until now administration hard-liners who favor "regime change" in Tehran and argue for consideration of military strikes to preempt the nuclear program have blocked those who favor joining the Europeans in talks. But regime change, though desirable, appears less likely than it did several years ago, because Iranian religious conservatives have triumphed over pro-democracy reformers. Military preemption -- a last resort in any case -- is complicated by a lack of intelligence about the location of Iranian nuclear sites as well as the heavy commitment of U.S. military resources to Iraq. For the past year the administration has sought to persuade the board of the International Atomic Energy Agency to refer Iran to the Security Council for possible sanctions because of its violations of the Nuclear Non-Proliferation Treaty. But this initiative, too, has gone nowhere.

The result is that the Bush team grumpily watches as the Europeans try to persuade Iran to end its steps toward enriching uranium or producing plutonium -- critical thresholds in the development of weapons -- in exchange for economic incentives and guarantees of fuel supplies for nuclear power and research reactors. A first agreement, reached a year ago, soon collapsed as the Iranians ruthlessly exploited its loopholes. Turning aside U.S. suggestions of sanctions or U.N. action, the Europeans persisted, but even if they reach another interim agreement, their diplomatic efforts probably won't succeed without American support. European inducements are unlikely to persuade Iran's rulers to permanently give up their nuclear ambitions as long as they perceive a threat from the United States. Nor is Iran likely to go along unless it is convinced that, in the absence of an agreement, the Europeans will join with the Bush administration in tougher measures.

Success in preventing an Iranian bomb consequently depends on the forging of a cohesive Western strategy founded on a restored U.S. relationship with Germany and France. Whether or not they finalize a new accord with Iran this week, the Europeans will need to commit themselves unambiguously to the principle that a nuclear-armed Iran is unacceptable -- which means that diplomatic failure must lead directly to sanctions. Mr. Bush, in turn, should agree to U.S. participation with the Europeans in any endgame of bargaining with Tehran. It may be a distasteful course, but it is preferable to doing nothing while a rogue state goes nuclear.