WASHINGTON — Iran halted its nuclear weapons development program in the fall of 2003 under international pressure but is continuing to enrich uranium, which means it may still be able to develop a weapon between 2010 and 2015, according to a new U.S. intelligence assessment released Monday.

That finding, part of a new National Intelligence Estimate on Iran, is a sharp turnaround from two years ago when U.S. intelligence agencies believed Tehran was determined to develop a nuclear weapons capability and was continuing its weapons development program. It suggests that Iran’s decisions are rational and pragmatic, and that Tehran is more susceptible to diplomatic and financial pressure than previously thought, the document concluded.

“Tehran’s decision to halt its nuclear weapons program suggests it is less determined to develop nuclear weapons than we have been judging since 2005,” the summary of the secret report says.

The findings come at a time of escalating tensions between the United States and Iran, which President Bush has labeled part of an “axis of evil.” On Oct. 17, Bush said, “If you’re interested in avoiding World War III, it seems like you ought to be interested in preventing them (Iran) from having the knowledge necessary to make a nuclear weapon.”

Rand Beers, who resigned from Bush’s National Security Council just before the Iraq war, said the report should derail any appetite for war on the administration’s part, and should reinvigorate regional diplomacy. “The new NIE throws cold water on the efforts of those urging military confrontation with Iran,” he said.

Senior intelligence officials said Monday they failed to detect Iran’s fall 2003 halt in nuclear weapons development in time to reflect it in the 2005 estimate.

One of the officials said Iran is the most challenging country to spy on — harder even than North Korea, a notoriously closed society. “We put a lot more collection assets against this,” the official said, “but gaps remain.”