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."

Such sentiment contrasts with the assertions of President Bush, who said as recently as April that "the development of a nuclear weapon in Iran is intolerable." He promised that a recalcitrant Iran "will be dealt with, starting through the United Nations."

The Iranians contend their nuclear experiments and their acquisition of sophisticated supplies are intended for peaceful atomic energy projects, not for building weapons. They point out that the nuclear Non-Proliferation Treaty permits nations to develop uranium-enrichment technology.

The Vienna-based IAEA has taken the lead in testing Iran's assertions, but the U.N. monitoring agency has said it cannot be certain what Iran intends.

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."

The vote represents a rejection of Iranian protests of unfair treatment and a strong endorsement of inspections designed to expose Iran's remaining nuclear mysteries.

Important figures in Iran quickly decried the vote, insisting that Iran was being targeted by a U.S.-led cabal. The resolution was introduced by France, Germany and Britain.

"We believe the agency acted based on the pressure from some of the political centers, particularly America," Foreign Minister Kamal Kharrazi told state television. An influential cleric, Ayatollah Mohammad Emamiv Kashani, said in a sermon broadcast on state radio that outsiders were overreacting.

"The West's political commotion about Iran's peaceful nuclear program is baseless," Kashani said.

The European diplomat described a "working assumption" abroad that Iran intends to acquire nuclear weapons and not forswear them, as the Libyans did in December, in return for U.S. and British assurances of improved economic and diplomatic ties.

"I don't think anyone expects them to do a Libya," he said.

The Bush administration inherited economic sanctions on Iran and continued a diplomatic freeze, with the exception of logistical discussions about the wars in Afghanistan and Iraq. The president himself labeled Iran a member of an "axis of evil."

Faced with the challenge of halting Iran's nuclear progress, however, U.S. officials describe their options as limited. They also say their ability to see inside Iran is extremely limited.

"The really hard problem with secretive states that are trying to acquire weapons of mass destruction is that you never know how much of the picture you're seeing. . . ," the senior White House official said. "You try to get as much international pressure as you can for a process that is really thorough and that is rigorous and has things like spot inspections."

Unlike Libya, Iran has developed an indigenous capacity to build key uranium-enrichment components. Experts say its range of suppliers is also greater than Libya's.

European foreign ministers tried to entice Iran into suspending its uranium-enrichment program last year, offering inducements in return for verifiable, if vague, steps. The agreement quickly stalled. The Europeans, backed by the IAEA, said Iran cheated; Iranian leaders said the Europeans reneged.

The Bush administration believes Iran's behavior merits forwarding the Iran case to the Security Council. Speaking Tuesday in Baltimore, Assistant Secretary of State John Wolf summed up the U.S. view: "While it proclaims fealty to the [Non-Proliferation Treaty], Iran is an active nuclear weapons wannabe."

One proliferation expert inside the administration said that referring the matter to the council in September would be unlikely to result in a strong punitive resolution, given the reluctance of the Russians and Chinese, among others. But it could help shame Iran and chill some foreign companies and governments from doing business there.

Yet pushing the matter to the Security Council so close to the U.S. presidential election would pose political risks and might not deter the Iranians, who see their nuclear effort as a point of national pride.

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.

The ever-shifting political firmament in Tehran is a factor in U.S. and European calculations -- and a ray of cautious hope.

Although some Iranian moderates are among the voices calling for Iran to develop a defensive nuclear option, policymakers abroad believe the desire of moderates for a greater opening to the West could deter Iran from building such weapons.

In this view, the best hope may be to slow Iran's program long enough for the hard-line religious leaders who run the country to pass from the scene. There is no indication yet, however, that the moderates are close to a triumph. In fact, their power has been steadily eroding.

Staff writer Glenn Kessler contributed to this report.