In an interview with The Associated Press, John Bolton, undersecretary of state for arms control, said that whether Saddam's regime actually possessed weapons of mass destruction "isn't really the issue."
"The issue I think has been the capability that Iraq sought to have ... WMD programs," Bolton said at the U.S. Embassy in Paris.
Bolton said that Saddam kept "a coterie" of scientists he was preserving for the day when he could build nuclear weapons unhindered by international constraints.
That fact, combined with Iraq's history of deceiving U.N. inspectors, showed that Saddam could not be trusted to abandon his ambition to develop unconventional weapons, Bolton said.
"Whether he possessed them today or four years ago isn't really the issue," he said. "As long as that regime was in power, it was determined to get nuclear, chemical and biological weapons one way or another."
"Until that regime was removed from power, that threat remained that was the purpose of the military action," added Bolton, who was in Paris for a two-day conference on interdiction of shipments of weapons of mass destruction.
Disarming Saddam Hussein was the Bush administration's top rationale for the war, which started in March, and officials said beforehand that they knew where weapons were hidden.
But they have not reported finding any weapons in five months of searching. Government officials, however, still express hope that evidence of weapons programs will be found in Iraq.
The lack of success so far, after warnings that Iraq posed an immediate danger, has led critics and some former government analysts to suggest the administration exaggerated the threat posed by Saddam.
During a news conference before the interview with the AP, Bolton said that CIA weapons adviser David Kay, who is leading the hunt for weapons, would soon release a new report on his mission.
He did not say whether he expected the report to contain proof of Iraqi weapons programs.
"I have been confident that under Saddam Hussein, the Iraqis were determined to break the U.N. inspections and sanctions regime," he told reporters. "And that that's why the elimination of Saddam Hussein's regime was critical, and the evidence to support that I think is there."