A new assessment by American intelligence agencies concludes that Iran halted its nuclear weapons program in 2003 and that the program remains on hold, contradicting an assessment two years ago that Tehran was working inexorably toward building a bomb.

The conclusions of the new assessment are likely to be major factor in the tense international negotiations aimed at getting Iran to halt its nuclear energy program. Concerns about Iran were raised sharply after President Bush had suggested in October that a nuclear-armed Iran could lead to "World War III," and Vice President Dick Cheney promised "serious consequences" if the government in Tehran did not abandon its nuclear program.