Chief U.S. weapons inspector Charles Duelfer says Iraq had no stockpiles of biological, chemical or nuclear weapons before last year's U.S.-led invasion. The Bush administration cited the threat of Iraqi weapons of mass destruction as a main reason for going to war.

Mr. Duelfer presented his conclusions in testimony before the Senate Armed Services Committee Wednesday. "I do not expect that militarily significant WMD stocks are hidden in Iraq," he said.

But at the same time, Mr. Duelfer lent support to the Bush administration's argument that deposed Iraqi leader Saddam Hussein remained a threat. He cited evidence that Saddam had not lost his ambition to pursue weapons of mass destruction, and hoped to revive the weapons program if United Nations sanctions were lifted.

"Those around Saddam seemed quite convinced that once sanctions were ended and all other things being equal, Saddam would renew his efforts in this field," he said.

Mr. Duelfer said Saddam argued that the use of chemical weapons saved his government by halting Iranian ground offensives during the Iran-Iraq war, and by threatening to use chemical and biological weapons, Saddam believes he deterred coalition forces from pressing on to Baghdad during the 1991 Gulf War.

Democrats, including President Bush's Democratic challenger for the White House, Senator John Kerry, have argued Mr. Bush rushed to war with Iraq last year without giving U.N. inspectors enough time to investigate.

The top Democrat on the Armed Services Committee, Senator Carl Levin of Michigan, used the opportunity to criticize the administration for changing the rationale for war when no weapons of mass destruction were found.

"After the war started, the administration began an effort to change the subject of the debate, from the actual presence of weapons of mass destruction, to WMD programs, then to WMD-related-program activities, and more recently, to speculation about intentions," he said.

But under questioning from the Republican chairman, Senator John Warner of Virginia, Mr. Duelfer said the world is better off now that Saddam Hussein is out of power.

There was a similar line of questioning from Senator John McCain, an Arizona Republican. "Is there any doubt in your mind that if Saddam Hussein were in power today, and there were no restrictions or sanctions placed on him, that he would be attempting to acquire weapons of mass of destruction, Mr. Duelfer?," asked the Senator.

"To me, that is quite clear," he answered.

Mr. Duelfer drew the conclusions in his report from documents, testimony from Iraqi officials, and debriefings with Saddam Hussein following his capture by U.S. forces.