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.