Iran’s progress at Fordo was disclosed by officials familiar with the findings of inspectors from the International Atomic Energy Agency who have been to the site recently as part of their regular visits. The officials included some from European governments who have opposed taking military action to slow the Iranian program, arguing that sanctions — with a mix of covert action — are far preferable.

The report comes at a moment when Iran has emerged as a point of contention in the foreign policy debates surrounding the approaching election. Mr. Romney has charged that the president has been “weak” on Iran, and said that Iran’s production of nuclear material had expanded greatly during Mr. Obama’s tenure. But he also embraced diplomacy in the debate on Monday.

Asked about the intelligence reports, Tommy Vietor, the spokesman for the National Security Council, said, “While we can’t comment on a report that has yet to be released, we remain concerned about Iran’s defiance of its international obligations.” He noted that “the president is determined to prevent Iran from getting a nuclear weapon and continues to believe there is time and space for diplomacy.”

Until just two months ago, Prime Minister Benjamin Netanyahu of Israel suggested he would not allow the Fordo plant to go into operation, warning that once it did Iran would have begun to enter a “zone of immunity” where it could produce nuclear fuel without fear of an Israeli strike. Israel does not possess the bunker-busting bombs that would be needed to destroy the facility, though the United States does have one weapon that can do the job: the “massive ordnance penetrator” that just entered the American arsenal.

In September, however, Israeli officials suddenly stopped using the “zone of immunity” phrase, and Mr. Netanyanu told the United Nations that he could wait until late spring before any taking military action, saying that was when Iran would be on the cusp of the ability to produce a bomb. European and American officials interpreted that announcement as evidence that Mr. Netanyahu concluded that Israel could not get through the more than 200 feet of rock over the Fordo plant without American help.