In an interview published on Tuesday, Powell told the Washington Post: "The absence of a stockpile changes the political calculus; it changes the answer you get."
But Powell conceded that the administration's conviction that Saddam already had banned weapons had made the case for war more urgent, the newspaper reported.
Asked if he would have recommended an invasion knowing Iraq had no prohibited weapons, Powell replied:
"I don't know, because it was the stockpile that presented the final little piece that made it more of a real and present danger and threat to the region and to the world."
Powell defended the Bush administration's decision to go to war, saying that history would ultimately judge that it "was the right thing to do," the newspaper said.
The Post said during the lengthy interview, Powell suggested that former chief weapons inspector David Kay's testimony last week before a Senate panel was more supportive of the administration than has been portrayed in news accounts.
"The absence of a stockpile changes the political calculus; it changes the answer you get"
Secretary of State, US
About his United Nations presentation last year which detailed Iraq's possible weapons stockpiles, Powell said it reflected the best judgments of all of the intelligence agencies.
The Post asked whether the American public should be reassured that so many intelligence agencies were so wrong.
Powell replied: "I think it should be reassuring to the voters of the United States that we found a regime that's clearly demonstrated intent and clearly had the capability, and that the president had the information from the intelligence community."
He added the people would understand that with the body of evidence available to the president at that time, he made a prudent decision.