WASHINGTON — Even as the United Nations’ nuclear watchdog said in a new report Friday that Iran had accelerated its uranium enrichment program, American intelligence analysts continue to believe that there is no hard evidence that Iran has decided to build a nuclear bomb.

Recent assessments by American spy agencies are broadly consistent with a 2007 intelligence finding that concluded that Iran had abandoned its nuclear weapons program years earlier, according to current and former American officials. The officials said that assessment was largely reaffirmed in a 2010 National Intelligence Estimate, and that it remains the consensus view of America’s 16 intelligence agencies.

At the center of the debate is the murky question of the ultimate ambitions of the leaders in Tehran. There is no dispute among American, Israeli and European intelligence officials that Iran has been enriching nuclear fuel and developing some necessary infrastructure to become a nuclear power. But the Central Intelligence Agency and other intelligence agencies believe that Iran has yet to decide whether to resume a parallel program to design a nuclear warhead — a program they believe was essentially halted in 2003 and which would be necessary for Iran to build a nuclear bomb. Iranian officials maintain that their nuclear program is for civilian purposes.

In Senate testimony on Jan. 31, James R. Clapper Jr., the director of national intelligence, stated explicitly that American officials believe that Iran is preserving its options for a nuclear weapon, but said there was no evidence that it had made a decision on making a concerted push to build a weapon. David H. Petraeus, the C.I.A. director, concurred with that view at the same hearing. Other senior United States officials, including Defense Secretary Leon E. Panetta and Gen. Martin E. Dempsey, the chairman of the Joint Chiefs of Staff, have made similar statements in recent television appearances.

“They are certainly moving on that path, but we don’t believe they have actually made the decision to go ahead with a nuclear weapon,” Mr. Clapper told the Senate Select Committee on Intelligence.

Critics of the American assessment in Jerusalem and some European capitals point out that Iran has made great strides in the most difficult step toward building a nuclear weapon, enriching uranium. That has also been the conclusion of a series of reports by the International Atomic Energy Agency’s inspectors, who on Friday presented new evidence that the Iranians have begun enriching uranium in an underground facility.

Once Iran takes further steps to actually enrich weapons grade fuel — a feat that the United States does not believe Iran has yet accomplished — the critics believe that it would be relatively easy for Iran to engineer a warhead and then have a bomb in short order. They also criticize the C.I.A. for being overly cautious in its assessments of Iran, suggesting that it is perhaps overcompensating for its faulty intelligence assessments in 2002 about Iraq’s purported weapons programs, which turned out not to exist. In addition, Israeli officials have challenged the very premise of the 2007 intelligence assessment, saying they do not believe that Iran ever fully halted its work on a weapons program.

Yet some intelligence officials and outside analysts believe there is another possible explanation for Iran’s enrichment activity, besides a headlong race to build a bomb as quickly as possible. They say that Iran could be seeking to enhance its influence in the region by creating what some analysts call “strategic ambiguity.” Rather than building a bomb now, Iran may want to increase its power by sowing doubt among other nations about its nuclear ambitions. Some point to the examples of Pakistan and India, both of which had clandestine nuclear weapons programs for decades before they actually decided to build bombs and test their weapons in 1998.

“I think the Iranians want the capability, but not a stockpile,” said Kenneth C. Brill, a former United States ambassador to the International Atomic Energy Agency who also served as director of the intelligence community’s National Counterproliferation Center from 2005 until 2009. Added a former intelligence official: “The Indians were a screwdriver turn away from having a bomb for many years. The Iranians are not that close.”

To be sure, American analysts acknowledge that understanding the intentions of Iran’s leadership is extremely difficult, and that their assessments are based on limited information. David A. Kay, who was head of the C.I.A.’s team that searched for Iraq’s weapons programs after the United States invasion, was cautious about the quality of the intelligence underlying the current American assessment.

“They don’t have evidence that Iran has made a decision to build a bomb, and that reflects a real gap in the intelligence,” Mr. Kay said. “It’s true the evidence hasn’t changed very much” since 2007, he added. “But that reflects a lack of access and a lack of intelligence as much as anything.”

Divining the intentions of closed societies is one of the most difficult tasks for American intelligence analysts, and the C.I.A. for decades has had little success penetrating regimes like Iran and North Korea to learn how their leaders make decisions.

Amid the ugly aftermath of the botched Iraq intelligence assessments, American spy agencies in 2006 put new analytical procedures in place to avoid repeating the failures. Analysts now have access to raw information about the sources behind intelligence reports, to help better determine the credibility of the sources and prevent another episode like the one in which the C.I.A. based much of its conclusions about Iraq’s purported biological weapons on an Iraqi exile who turned out to be lying.

Analysts are also required to include in their reports more information about the chain of logic that has led them to their conclusions, and differing judgments are featured prominently in classified reports, rather than buried in footnotes.

When an unclassified summary of the 2007 intelligence estimate on Iran’s nuclear program was made public, stating that it had abandoned work on a bomb, it stunned the Bush administration and the world. It represented a sharp reversal from the intelligence community’s 2005 estimate, and drew criticism of the C.I.A. from European and Israeli officials, as well as conservative pundits. They argued that it was part of a larger effort by the C.I.A. to prevent American military action against Iran.

The report was so controversial that many outside analysts expected that the intelligence community would be forced to revise and repudiate the estimate after new evidence emerged about Iran’s program, notably from the United Nations’ inspectors. Yet analysts now say that while there has been mounting evidence of Iranian work on enrichment facilities, there has been far less clear evidence of a weapons program.

Still, Iran’s enrichment activities have raised suspicions, even among skeptics.

“What has been driving the discussion has been the enrichment activity,” said one former intelligence official. “That’s made everybody nervous. So the Iranians continue to contribute to the suspicions about what they are trying to do.”

Iran’s efforts to hide its nuclear facilities and to deceive the West about its activities have also intensified doubts. But some American analysts warn that such behavior is not necessarily proof of a weapons program. They say that one mistake the C.I.A. made before the war in Iraq was to assume that because Saddam Hussein resisted weapons inspections — acting as if he were hiding something — it meant that he had a weapons program.

As Mr. Kay explained, “The amount of evidence that you were willing to go with in 2002 is not the same evidence you are willing to accept today.”