At the same time, they acknowledge that in retrospect, some of its conclusions appear to have been thinly sourced and were based on methods less rigorous than were ultimately required under an intelligence overhaul that did not begin in earnest until later.

It was also written by some of the same team that had produced key parts of the flawed Iraq estimate. Robert D. Walpole oversaw both reports as the national intelligence officer responsible for assessing illicit-weapons programs.

Robert Hutchings, who as head of the National Intelligence Council from 2003 to early 2005 oversaw early production of the 2005 Iran assessment, said the quality of information about Iran’s nuclear program should have made American intelligence analysts wary of judging anything with “high confidence.” That was how the 2005 report described the basis for its assertion that Iran was determined to develop nuclear weapons, a conclusion that has been disavowed.

“The fact that we’ve reversed course two years later suggests that the high confidence back then wasn’t warranted,” said Mr. Hutchings, who had left the intelligence council by the time the intelligence estimate was produced in May 2005.

Paul R. Pillar, another member of the National Intelligence Council in 2005, said it was a “fair point” to criticize intelligence agencies for overstating their confidence in the judgments of the 2005 estimate. But he said the judgment that Iran is determined to obtain the bomb could prove correct in the long run.