Details in Military Notes Led to Shift on Iran, U.S. Says

WASHINGTON, Dec. 5 — American intelligence agencies reversed their view about the status of Iran’s nuclear weapons program after they obtained notes last summer from the deliberations of Iranian military officials involved in the weapons development program, senior intelligence and government officials said on Wednesday.

The notes included conversations and deliberations in which some of the military officials complained bitterly about what they termed a decision by their superiors in late 2003 to shut down a complex engineering effort to design nuclear weapons, including a warhead that could fit atop Iranian missiles.

The newly obtained notes contradicted public assertions by American intelligence officials that the nuclear weapons design effort was still active. But according to the intelligence and government officials, they give no hint of why Iran’s leadership decided to halt the covert effort.

Ultimately, the notes and deliberations were corroborated by other intelligence, the officials said, including intercepted conversations among Iranian officials, collected in recent months. It is not clear if those conversations involved the same officers and others whose deliberations were recounted in the notes, or if they included their superiors.

The American officials who described the highly classified operation, which led to one of the biggest reversals in the history of American nuclear intelligence, declined to describe how the notes were obtained.

But they said that the Central Intelligence Agency and other agencies had organized a “red team” to determine if the new information might have been part of an elaborate disinformation campaign mounted by Iran to derail the effort to impose sanctions against it.

In the end, American intelligence officials rejected that theory, though they were challenged to defend that conclusion in a meeting two weeks ago in the White House situation room, in which the notes and deliberations were described to the most senior members of President Bush’s national security team, including Vice President Dick Cheney.

“It was a pretty vivid exchange,” said one participant in the conversation.

The officials said they were confident that the notes confirmed the existence, up to 2003, of a weapons programs that American officials first learned about from a laptop computer, belonging to an Iranian engineer, that came into the hands of the C.I.A. in 2004.

Ever since the major findings of the new National Intelligence Estimate on Iran’s nuclear program were made public on Monday, the White House has refused to discuss details of what President Bush, in a news conference on Tuesday, termed a “great discovery” that led to the reversal........