WASHINGTON – A last-minute demand from Iranian negotiators could scuttle a European deal with the Islamic Republic to halt uranium enrichment activities in exchange for technical support down the road.

Iranian negotiators at the International Atomic Energy Agency demanded yesterday the right to exempt some 20 centrifuges from international inspections the envoys claimed was for experimental purposes. The position is at odds with a promise from the mullahs to halt uranium enrichment altogether made on Sunday.

Even the often conciliatory director general of the IAEA, Mohamed ElBaradei, could not bring himself to give Iran a clean bill of nuclear health in his report to the agency’s board of governors.

“On Iran, I am going to report that we have completed our work with regard to the verification of the suspension with one exception, and that is the request by Iran to exempt 20 centrifuges for R&D without using nuclear materials,” he said at a press briefing yesterday in Vienna.

Mr. ElBaradei’s report to the board of governors also said that he has yet to receive adequate explanations for uranium contamination on equipment, a question that has plagued the agency since 2003 when Iran submitted to inspections of its previously undeclared facilities for enriching nuclear fuel.

The issue is important because it could disclose new clues about the nature and depth of the international black market that supplied the equipment and material for the program Iran had kept concealed until last year. A recent CIA report says that Pakistani nuclear scientist A. Q. Khan provided the Iranians with designs for older Pakistani centrifuges.

Mr. ElBaradei’s statement to his board of governors says, “There remain two important issues, concerning Iran’s past undeclared program, that are relevant to the Agency’s ability to provide assurance that there are no undeclared enrichment activities in Iran: the origin of the low enriched and high enriched uranium particle contamination found at various locations in Iran; and the extent of Iran’s efforts to import, manufacture and use centrifuges of both the P-1 and P-2 designs.”

While Mr. ElBaradei said he had made progress on tracking the origin of the equipment and source of contamination, he could not yet conclude “there are no undeclared nuclear materials or activities in Iran.”

The question of undisclosed locations also worries the CIA. On November 23, the CIA released an unclassified report on proliferation that said Iran’s existing technology in locations hidden from the IAEA.

“During 2003, Iran continued to pursue an indigenous nuclear fuel cycle ostensibly for civilian purposes but with clear weapons potential,” the report says.

It also says that IAEA inspections would keep the nuclear technology from a weapons program at the sites the Islamic Republic has already submitted for international inspection.

“However, Iran could use the same technology at other, covert locations for military applications,” the report warns.

The president this week said he is concerned Iran is building an atom bomb and his outgoing secretary of state, Colin Powell, has said recently that Iran is testing long-range missiles to deliver the weapon. The public statements from high-level American officials and the president cast doubt on the Iranian regime’s contention that it has invested so much time and effort to find an alternative source of energy, an already suspect argument coming from a government that controls some of the largest reserves of petroleum in the world.

The White House had hoped the unresolved questions about contamination and origin of equipment would lead Mr. ElBaradei to conclude Iran is in violation of the nuclear nonproliferation treaty and refer the lapse to the U.N. Security Council, a body that can authorize sanctions, embargoes, and even war.

This month, however, Mr. Powell said America supports the efforts of France, Germany, and the United Kingdom to broach a deal to pause Iran’s enrichment process. But as a part of that deal, American diplomats have demanded that any Iranian violation of the new agreement trigger an automatic referral to U.N. Security Council.

Iran’s negotiators however, have balked at those demands, according to wire service accounts, leading the Europeans to drop it from the most recent drafts.

Yesterday, Mr. ElBaradei predicted the disagreements between Iranian negotiators and the Europeans would be resolved by today.

This, however, may give many American officials pause because Mr. ElBaradei has been perceived as not only hostile to the Bush administration but too soft on Iranian proliferation.

Over the summer, signals intelligence, disputed by some intelligence agencies, suggested that behind the scenes Mr. ElBaradei was coaching Iranian diplomats on how to best adhere to the letter of the nuclear nonproliferation treaty and avoid international censure in the press.

A former Iranian analyst for the Pentagon, Michael Rubin, said in an interview Wednesday, “The fact that ElBaradei was caught coaching the Iranians on how to spin the Western press demonstrates the bankruptcy of the IAEA as a regulatory agency. When we give information to the IAEA, often people like ElBaradei will use it to teach the Iranians how to conceal their programs.”