WASHINGTON, Dec. 3 — A new assessment by American intelligence agencies concludes that Iran halted its nuclear weapons program in 2003 and that the program remains frozen, contradicting judgment two years ago that Tehran was working relentlessly toward building a nuclear bomb.

The conclusions of the new assessment are likely to reshape the final year of the Bush administration, which has made halting Iran’s nuclear program a cornerstone of its foreign policy.

The assessment, a National Intelligence Estimate that represents the consensus view of all 16 American spy agencies, states that Tehran is likely keeping its options open with respect to building a weapon, but that intelligence agencies “do not know whether it currently intends to develop nuclear weapons.”

Iran is continuing to produce enriched uranium, a program that the Tehran government has said is designed for civilian purposes. The new estimate says that enrichment program could still provide Iran with enough raw material to produce a nuclear weapon sometime by the middle of next decade, a timetable essentially unchanged from previous estimates.