"America is safer today with Saddam Hussein in prison," Mr. Bush said in a surprise statement to reporters as he prepared to fly to Wisconsin.
"Much of the accumulated body of our intelligence was wrong and we must find out why," Mr. Bush said.
But, he maintained that the Iraqi leader retained the "means and the intent" to produce weapons of mass destruction.
The report of weapons hunter Charles Duelfer was presented Wednesday to senators and the public in the midst of a fierce presidential election campaign in which Iraq and the war of terror have become the overriding issues.
As CBS National Security Correspondent David Martin reports, Duelfer's report renders pre-war statements by Mr. Bush and his senior advisers flat wrong. Democrats saw their opening and took it.
"In short, we invaded a country, thousands of people have died, and Iraq never posed a grave or growing danger," said Democratic Sen. Jay Rockefeller of West Virginia on Wednesday. A spokesman for Democrat John Kerry, said the report "underscores the incompetence of George Bush's Iraq policy."
But British Prime Minister Tony Blair, traveling in Africa, said the report shows Saddam was "doing his best" to evade the U.N. sanctions.
Mr. Bush took a similar line on Thursday.
"The Duelfer report showed that Saddam was systematically gaming the system, using the U.N. oil for food program to try to influence countries and companies in an effort to undermine sanctions," Mr. Bush said. "He was doing so with the intent of restarting his weapons program once the world looked away."
The president's tone echoed a he gave the day before, in which he did not mention the Duelfer report but did accuse Kerry of having "a strategy of retreat."
The chief U.S. weapons hunter found that Saddam's weapons of mass destruction programs had deteriorated into only hopes and dreams by the time of the U.S.-led invasion last year, a decline wrought by the first Gulf War and years of international sanctions.
Interviews with Saddam and other former Iraqi officials made clear to inspectors that the dictator had not lost his ambition to pursue weapons of mass destruction and hoped to revive his weapons program if sanctions were lifted, the report said. But Saddam wanted the weapons primarily not to attack the United States or to provide them to terrorists, but to oppose his older enemies, Iran and Israel.
The report chronicles the decay of Iraq's chemical, biological and nuclear weapons programs after its defeat in the 1991 Gulf War.
By the late 1990s, only its long-range missile efforts continued in defiance of the United Nations; even then, Iraq's ballistic and cruise missile designs had not proceeded far past the drawing board. Saddam's other plans would have to wait until he was free of the sanctions and free of international attention.
Duelfer's Iraq Survey Group drew on interviews with senior Iraqi officials, 40 million pages of documents and classified intelligence to conclude that Iraq destroyed its undeclared chemical and biological stockpiles under pressure of U.N. sanctions by 1992 and never resumed production.
The U.S.-led invasion pushed one of Iraq's leaders into seeking chemical weapons to defend the country. But it doesn't appear that Saddam's son Odai located any.
Iraq ultimately abandoned its biological weapons programs in 1995, largely out of fear they would be discovered and tougher enforcement imposed.
"Indeed, from the mid-1990s, despite evidence of continuing interest in nuclear and chemical weapons, there appears to be a complete absence of discussion or even interest in BW at the presidential level," according to a summary of Duelfer's 1,000-page report.
And Iraq also abandoned its nuclear program after the war, and there was no evidence it tried to reconstitute it. Saddam's intentions to restart his weapons programs were never formalized.
"The former regime had no formal written strategy or plan for the revival of WMD after sanctions," the summary says. "Neither was there an identifiable group of WMD policymakers or planners separate from Saddam. Instead his lieutenants understood WMD revival was his goal from their long association with Saddam and his infrequent, but firm, verbal comments and directions to them."
Duelfer's findings contradict most of the assertions by the Bush administration and the U.S. intelligence community about Iraq's threat in 2002 and early 2003.
Mr. Bush said in October 2002 that, "Saddam Hussein still has chemical and biological weapons and is increasing his capabilities to make more." Mr. Bush also said then, "The evidence indicates that Iraq is reconstituting its nuclear weapons program."
Vice President Dick Cheney, in a speech on Aug. 26, 2002, 6 1/2 months before the invasion, made similar charges. "Simply stated, there is no doubt that Saddam Hussein now has weapons of mass destruction," he said.
The United States led an invasion into Iraq in March 2003, taking the capital, Baghdad, within weeks. Since then, the United States and its allies have fought a dangerous insurgency of Iraqis as well as Islamic extremists who have come to Iraq to kill Americans.
Some 1,196 coalition personnel have been killed since the start of the war. Of those, 1,060 are American, 67 British and 69 are from other coalition countries. Unknown numbers of Iraqis have also died on both sides of the conflict.
Before the war, Saddam's chief success was in manipulating a U.N. that began in 1996 to avoid the sanctions' effects for a few years, acquiring billions of dollars to import goods such as parts for missile systems.
Duelfer told Congress on Wednesday that sanctions against Saddam — even though they appeared to work in part — were unsustainable long term. However, the erosion of sanctions stopped after the Sept. 11, 2001, attacks, Duelfer found, preventing Saddam from pursuing weapons of mass destruction.