By CRAIG S. SMITH
VIENNA - The United States lobbied Monday to toughen an International Atomic Energy Agency draft resolution on Iran's nuclear program, hoping to include a clear "trigger" that would send Iran's case to the United Nations Security Council for possible sanctions if the country fails to comply with I.A.E.A. demands by November.
The proposed resolution, prepared by Britain, France and Germany, gives Iran a November deadline to clarify inconsistencies in its nuclear energy program, suspected of masking efforts to build a bomb. But it falls short of setting specific requirements or explicitly threatening to send the case to the Security Council.
Nonetheless, the draft resolution is the toughest yet in a yearlong effort to persuade Iran to cooperate more fully with the United Nations nuclear agency and shows a shift in Europe's attitude toward Iran. The three European countries have in the past resisted American pressure to deliver a harsher rebuke to Iran.
"The Europeans are taking a very hard line now," said a European diplomat involved in the negotiations who spoke on condition of anonymity.
Iran warned Monday that it might resume efforts to produce highly enriched uranium that could be used to build a nuclear bomb if the United Nations continues pressuring it over its nuclear program. In March, Iran voluntarily agreed to suspend them.
"We can't imagine that the suspension will last very long," Hossein Mousavian, head of the Iranian delegation, told reporters at the I.A.E.A. headquarters here. He reiterated Iran's stance that under the Nuclear Nonproliferation Treaty it has the right to produce fuel for nuclear reactors.
The United States and other countries, however, have long pointed to inconsistencies in Iran's program.
Despite the suspension Iran promised in March, it has never halted the manufacture of centrifuge parts by private workshops. This month, Iran said it planned to convert about 40 tons of "yellow cake" uranium into uranium hexafluoride gas, the raw material for centrifuge enrichment. Nuclear experts warned that the quantity involved was sufficient to produce fuel for several bombs.
The draft resolution circulated by the three European countries calls on the I.A.E.A. chief, Dr. Mohamed ElBaradei, to produce a full report on Iran's nuclear activities before the next meeting of the agency's board of governors. It states that on the basis of that report, the board will make "a definitive determination on whether or not further steps are required."
Everyone involved understands that those "further steps" include referral to the Security Council, which could lead to sanctions against Iran. The United States, which has lobbied for tougher action against Iran since details of its clandestine nuclear program were disclosed last year, is working to harden the resolution's language further and to include a clear trigger for action in November by giving Iran a list of requirements, like a comprehensive suspension of enrichment activity, that it must fulfill before then.
In Washington, a senior Bush administration official said the United States would still like the I.A.E.A. to refer the issue to the Security Council this month, rather than wait until November. But European diplomats say that the United States has little choice, because there are not the votes on agency's board of governors for a quicker referral.
Once the United States and the three European countries have agreed on the draft, the resolution will be submitted to the board for approval this week. The board can call for a vote, but resolutions are usually approved by consensus to avoid politicizing the agency's decisions.
Iran, which is not on the 35-member board, is negotiating with Britain, France and Germany to soften the resolution in return for renewed commitments on suspending some of its activities.
Iran continues to insist that its nuclear program is for purely peaceful purposes. But the discovery two years ago that its program was much broader than it had disclosed to the United Nations agency and contained inadequately explained irregularities have convinced the United States that the oil-rich country's goal is not to produce cheap energy but to manufacture nuclear weapons.
Some Iranian equipment, for example, was found to be contaminated with weapons-grade uranium, and Iran had worked on producing polonium 210, a radioactive isotope that can help set off a nuclear explosion.
"There's a whole host of activities that in our opinion don't have anything to do with putting electricity into a light bulb," one Western official said.
Meanwhile, Dr. ElBaradei gave the board additional information on South Korea's secret nuclear experiments, disclosed this month, calling them "a matter of serious concern."
He said that South Korea had produced about 330 pounds of "natural uranium metal" at three secret facilities in the 1980's and that some of the metal was used in laser-based enrichment experiments in 2000 to produce a small amount of enriched uranium.
The disclosure suggests that South Korea's nuclear experiments had a longer history than previously thought, though South Korea contends that rogue scientists were responsible. Dr. ElBaradei said he would deliver a fuller report on South Korea in November.
Steven R. Weisman contributed reporting from Washington for this article.