Frustrated by evidence that Iran is still hiding elements of its nuclear program, the International Atomic Energy Agency rebuked the Tehran government yesterday for failing to cooperate fully with international investigators.

The United Nations agency's 35-member board declared unanimously that Iranian authorities had broken their promises of complete disclosure and called on Iran to act "on an urgent basis" to answer questions about its atomic ambitions and achievements.

Bush administration officials, convinced that Iran is developing nuclear weapons in defiance of international demands, claimed the sharply worded IAEA resolution as a victory. The measure does not, however, provide for any penalties, deadlines or guarantees that the matter will be referred to the U.N. Security Council, as the White House had wished.

Instead, the resolution comes amid growing doubts among U.S. officials and foreign allies about their ability to stop Iran from acquiring nuclear weapons. Diplomats and U.S. officials say that without a workable military option or an international consensus to punish Iran, their goal is to slow Iran's progress while searching for a change in Tehran's thinking.

A senior White House official, asked this week whether the administration can realistically expect to halt Iran's nuclear program, said, "I don't think we know the answer." The official declined to be quoted by name because of the sensitivity of the issue.

"We want Iran to renounce its nuclear ambitions," said a European diplomat who focuses on Iran. "We're all equally clear that there's no prospect of that happening, at least in the near term."...

....In the past 18 months, inspectors have uncovered an escalating series of contradictions in Iranian statements, along with evidence that nuclear experts consider strongly suggestive of a clandestine nuclear weapons program.

"The Iranians are serious about this nuclear weapons program," Robert Einhorn, a Clinton administration proliferation specialist, said yesterday. "They've been at it over 18 years. They've expended a vast amount of energy and financial resources to make it work. They're not going to abandon it lightly."

IAEA inspectors contend that Iran has repeatedly misstated details about its nuclear program and pursued enrichment technology in violation of pledges made to European foreign ministers in October. They accused Iran of offering contradictory evidence and often admitting details only when presented with undeniable evidence.

Even as the board met, the IAEA was investigating satellite images that suggested to U.S. government analysts that Iran was concealing nuclear activities in Tehran. U.S. diplomats, who favor a harder line than other countries, said the latest report showed Iran violating international obligations.

The IAEA board used strong words in the diplomatic world, saying it "deplores" the limits of Iran's cooperation. Iranian cooperation, the board said, had not been "as full, timely and proactive as it should have been."...

...In a private meeting at the Brookings Institution in early May, Iran's ambassador to the United Nations, Mohammed Javad Zarif, delivered a sharp message to influential Republicans and Democrats: We can make life easier for you in Iraq if you give Iran's nuclear program a pass.

Zarif's suggestion took several participants by surprise. It also demonstrated Iran's belief that it has greater leverage now that the United States is preoccupied with Iraq, home to Muslim Shiites with close ties to Iran...