Iran acknowledged yesterday that it had failed to comply with international nuclear nonproliferation rules, as documented in a harshly critical report by a U.N. agency. But Tehran asserted that the failures were minimal and rejected suggestions that it was developing nuclear weapons.

"The failures that Iran has been reproached for are minor, and are only on the order of the gram or milligram, while in the past some countries had problems with larger quantities of plutonium," Iran's representative to the International Atomic Energy Agency, Ali Akbar Salehi, was quoted as saying by state television.

The IAEA's confidential report said Iran manufactured small amounts of enriched uranium and plutonium as part of a nuclear program it operated in secret for 18 years. The report faulted Iran for hiding evidence of its nuclear program from international inspectors and for numerous breaches of its nuclear treaty obligations.

The U.N. nuclear watchdog said it would continue to probe whether Tehran's nuclear program was intended to develop weapons.

While the report said Iran had been misleading the IAEA as recently as last month, Salehi said the "matter is closed" because "these failures correspond to the past [and] corrective measures have been taken." Iran's failures, he said, only concerned "experiments in laboratories which we should have declared to the agency."

Salehi said "a very small quantity of plutonium" resulted as "a secondary effect" of producing medicine for hospitals. The IAEA report said Iran told investigators the experiments were designed to study the nuclear fuel cycle and gain experience in reprocessing.

The State Department and the White House would not comment yesterday on the report -- written for a Nov. 20-21 IAEA board meeting -- because the document had not been officially released. But a State Department spokesman, who spoke on condition of anonymity, said the report reinforced the Bush administration's concerns about Iran's nuclear program. "Iran's nuclear weapons program and its now well-documented pattern of [nuclear Non-Proliferation Treaty] safeguards violations are deeply troubling," the spokesman said.

He added that while Iran satisfied lingering questions, "we believe no country should be engaged in nuclear cooperation with Iran." But Russian officials said yesterday that Iran's recent cooperation with international inspectors -- and its willingness to allow unannounced inspections -- should demonstrate that Russia's construction of a nuclear power plant near the Iranian town of Bushehr did not pose a danger.

Indeed, experts said, Iran's willingness to signal cooperation with the IAEA might undercut U.S. efforts to maintain pressure on Iran. Washington could, for example, have the IAEA refer Iran's breaches of the non-proliferation treaty to the U.N. Security Council.

Robert Einhorn, a former assistant secretary of state for nonproliferation, said Iran now faced a "fundamental choice" that would decide not only its nuclear future but its place in the world.

"Which path Iran chooses depends to a great degree on how the international community behaves," said Einhorn, a senior advisor at the Center for Strategic and International Studies. "It is the job of the United States, Russia and the Europeans to remain united and to make it clear that going down the nuclear path is not the right path."

The Iranian opposition group that exposed Iran's uranium program at Natanz a year ago contends that Iran still has not told the full truth. Alireza Jafarzadeh, a former spokesman for the National Council of Resistance of Iran, an organization that was declared a terrorist group by the Bush administration over the summer, said the Iranian military remained heavily involved in directing the country's nuclear scientists, in contrast with Iran's assurances that the program is strictly peaceful.