Iran defended its failure to report the importation of a small amount of uranium by saying, in effect, that everybody does it.

Speaking to the board of the International Atomic Energy Agency, the Iranian representative, Ali Salehi, recited from an agency report that listed failures by many other countries to meet inspection standards.

"Hardly any member state can claim to be impeccable," Salehi said, according to a transcript of his remarks.

That response did not placate the United States, which expressed "grave concern" about Iran's nuclear ambitions, saying Tehran had only admitted to its plans when forced into it by public disclosure.

"Without the outside revelations, Iran's extensive nuclear program would still be proceeding on a largely clandestine basis," the U.S. ambassador, Kenneth Brill, said.

[President Bush said Wednesday that he and other world leaders would not tolerate nuclear weapons in Iran, The Associated Press reported from Washington. "The international community must come together to make it very clear to Iran that we will not tolerate construction of a nuclear weapon," Bush said. "Iran would be dangerous if it had a nuclear weapon." ]

Brill, noting that Iran had tested its capability to produce uranium metal - a necessary component for a nuclear bomb - asked the agency whether it was confident that Iran was not diverting nuclear material from its declared goal of power generation into a weapons program.

He said the United States favored a special inspection by the agency to scrutinize whether Iran had diverted material.

"The U.S. expects the agency's accumulation of further information will point to only one conclusion: that Iran is aggressively pursuing a nuclear weapons program," Brill concluded.

The strong words came even as the United States backed away from a campaign for a resolution demanding that Iran accept stricter supervision of its nuclear activities. Such a step would have required a majority vote of the agency's 35-member board, which the United States could not get.

While Britain and Canada also scolded Iran, a group of countries led by Malaysia came to Tehran's defense, saying it had been cooperative and transparent in its dealings with the agency.

"There are many other countries that have failed to report - not just Iran," said the Malaysian ambassador, Hussein Haniff. "They are now showing their willingness to cooperate."

Diplomats said they still expected the board to issue a statement on Thursday that would urge Iran to accept the expanded agency supervision - known as an additional protocol - without conditions.

Such a step, while not requiring a vote, would send a stronger signal than the board's usual practice after a debate, in which the chairman simply summarizes the various positions.

"The net effect of all this is to sharpen the spotlight on what's going on in Iran," said one Western diplomat. "I think it's fair to say the noose is tightening around Iran."

This week's debate followed a critical report by the agency's director-general, Mohamed ElBaradei, which said Iran had not been forthcoming about its activities, which have included the importation of uranium and the construction of two large nuclear facilities.

The report also said Iran denied a request by the agency to conduct environmental sampling at the Kalaye Electric Co., where it produces components for centrifuges. The samples would determine whether Iran used nuclear material to test the centrifuges in what is supposed to be a non-nuclear facility.

Iran faulted the report for reflecting the hard-line views of "certain influential capitals" - a clear reference to Washington.

"Our assessment is that the report could have been crafted in a more partial, fair, and balanced manner," Salehi said.

Western diplomats applauded the report for being uncommonly clear and forthright. But they added that the agency must keep up the pressure. ElBaradei is scheduled to present a final report on Iran's behavior by September. Brill said the agency should consider moving up the deadline.

Iran said this week that it was open to accepting broader agency supervision. But it has tied the move to gaining access to nuclear technology. The United States and other countries reject that quid pro quo.

"If Iran's nuclear program were limited only to peaceful purposes, Iran would see the additional protocol as a way to show its commitment to the non-proliferation regime and complete transparency," Brill said.