But the new report essentially disavows a judgment that the intelligence agencies issued in 2005, which concluded that Iran had an active secret arms program intended to transform the raw material into a nuclear weapon. The new estimate declares instead with “high confidence” that the military-run program was shut in 2003, and it concludes with “moderate confidence” that the program remains frozen. The report judges that the halt was imposed by Iran “primarily in response to increasing international scrutiny and pressure.”

It was not clear what prompted the reversal. Administration officials said the new estimate reflected conclusions that the intelligence agencies had agreed on only in the past several weeks. The report’s agnosticism about Iran’s nuclear intentions represents a very different tone than had been struck by President Bush, and by Vice President Dick Cheney, who warned in a speech in October that if Iran “stays on its present course, the international community is prepared to impose serious consequences.”

The estimate does not say when intelligence agencies learned that the arms program had been halted, but officials said new information obtained from covert sources over the summer had led to a reassessment of the state of Iran’s nuclear program and a decision to delay preparation of the estimate, which had been scheduled to be delivered to Congress in the spring.

The new report came out just over five years after a 2002 intelligence estimate on Iraq concluded that it possessed chemical and biological weapons programs and was determined to restart its nuclear program. That estimate was instrumental in winning the Congressional authorization for a military invasion of Iraq, but it proved to be deeply flawed, and most of its conclusions turned out to be wrong.

Intelligence officials said the specter of the 2002 estimate on Iraq hung over their deliberations on Iran even more than it had in 2005, when the lessons from the intelligence failure on Iraq were just beginning to prompt spy agencies to adapt a more rigorous approach to their findings.