“For now, the talks are dead in the water,” one senior official said Thursday.

Mr. Obama and his staff have been trying to avoid a crisis over Iran that would unfold in the last months of the presidential election. But the report, expected to be the last by the I.A.E.A. before Election Day, will lay out a stark reality: Despite increasingly painful sanctions, and a covert program called Olympic Games that aimed to slow the Iranian program with cyberattacks, Iran has made substantial progress in producing enriched uranium in recent years — from about one bomb’s worth when Mr. Obama took office in 2009 to the equivalent of about five bombs’ worth today.

But the fuel would require considerable additional enrichment before it was usable in a weapon, and even then, Mr. Obama and others have insisted, the United States would almost certainly have considerable notice, and time to act, before Iran developed a usable nuclear weapon. On this point, the Israelis disagree. The critical question likely to be prompted by the I.A.E.A. report, which could be published as soon as Wednesday, comes down to this: How much closer is Iran to gaining a nuclear weapons “capability” — that is, the ability to produce a bomb on relatively short notice?

The Israelis have declared that Iran cannot be permitted to reach that capability, a position Mr. Romney seemed to endorse during his visit to Israel. Mr. Obama has said only that he would prevent Iran from obtaining a weapon, and has left unclear whether it would be worth the risks to stop Iran from walking up to the edge of building a weapon.

This summer, two top administration officials, Defense Secretary Leon E. Panetta and the president’s national security adviser, Thomas E. Donilon, made separate visits to Israel to convince Mr. Barak and Prime Minister Benjamin Netanyahu that Mr. Obama meant it when he said he would stop Iran from obtaining a weapon.

But Israeli officials have made it clear that they have found the reassurances less than convincing, and suggested they might act even if the limits of Israel’s military power may mean the Iranian program would be delayed by only two years or so. Many in Israel’s military and intelligence establishments have argued that this is not the time for an attack, and the recently retired chief of staff of the Israeli Defense Force, Gabi Ashkenazi, added his voice on Wednesday to the former officials urging Mr. Netanyahu to look for other options, from further sanctions to additional covert action.

The Israeli case that the West may not be able to detect Iran’s progress could be fueled by another element of the forthcoming report, detailing efforts by Iran to clean up a long-suspected nuclear site called Parchin on the outskirts of Tehran.

It is at that site that the agency, based on interviews with at least one scientist and intelligence reports provided by Western powers, suspects Iran may have conducted weapons-related testing. But satellite imagery suggests that Iran has spent months cleaning up the site, even carting away topsoil. Diplomats believe that by the time I.A.E.A. inspectors are permitted to visit — if such a visit is allowed — whatever evidence was there could have been eradicated.