For years, Washington had based its assessment that Iran was pursuing nuclear weapons largely on its steady work to enrich uranium, which could be used for bombs but which Iran says it wants to fuel power reactors. Forcing Iran to give up enrichment became the goal.

The December estimate, by contrast, focused on weapons design. Based on fresh intelligence that Iran’s bomb design program was suspended in 2003, it said Iran was not pursuing nuclear weapons, even though uranium enrichment continued.

Perhaps no one exemplifies the debate more than Mike McConnell, the director of national intelligence, who has backpedaled from the conclusions of the intelligence estimate — even though he supervised it.

The report said intelligence analysts did not know enough to say whether Iran “currently intends to develop nuclear weapons.” But on February 26, McConnell told a radio interviewer, “Our estimate is they intend to have a nuclear weapon.” McConnell declined to comment for this article.