"Iraq had a weapons program," Mr. Bush said. "Intelligence throughout the decade shows they had a weapons program," he told reporters during a Cabinet meeting. "I am absolutely convinced that with time, we'll find out they did have a weapons program."
Weeks of searches in Iraq by military experts have not validated the administration's portrayal of Iraq's cache of weapons. Alleged stockpiles chemical and biological weapons have not turned up, nor has significant evidence of a nuclear weapons program.
Mr. Bush was asked whether American credibility was on the line in the hunt for illicit weapons. In answering, he pointed to the outcome of the war, not the weapons search.
"The credibility of this country is based upon our strong desire to make the world more peaceful, and the world is now more peaceful after our decision," he said.
Mr. Bush also insisted that al Qaeda had a presence in Baghdad.
"History will show, history and time will prove that the United States made the absolute right decision in freeing the people of Iraq from the clutches of Saddam Hussein," Mr. Bush said.
Sen. Carl Levin of Michigan, top Democrat on the Senate Armed Services Committee, said Sunday he wants a full congressional investigation. "I think that the nation's credibility is on the line, as well as (Mr. Bush's)," he said.
Asked about a joint congressional inquiry, White House spokesman Ari Fleischer said: "It's appropriate for Congress to look at it."
But, he added, lawmakers have already seen much of the intelligence that led the administration to invade Iraq.
Bush administration officials say they are confident proof will emerge that Saddam Hussein possessed the chemical and biological weapons cited as a key reason to invade Iraq.
"We have thousands and thousands and thousands of documents that we've not yet gone through," national security adviser Condoleezza Rice said Sunday. More sites need to be investigated and many more Iraqis must be interviewed about Saddam's weapons capabilities, she added.
"We will put together this whole picture, but the preponderance of evidence is that this was a regime that had the capability, that had unaccounted-for stockpiles and unaccounted-for weapons," Rice told CBS' "Face the Nation."
The discovery of two Iraqi truck trailers, equipped with fermenters, is the strongest U.S. evidence to date that Iraq had a biological weapons program; no actual weapons have been found.
Meanwhile, an International Atomic Energy Agency team continued a second day of inspections Monday at a complex in the vast Tuwaitha nuclear agency compound about 12 miles south of Baghdad.
The seven-member IAEA team is working under tight U.S. military escort and, as CBS News reports, under strict guidelines from the Pentagon, which does not want to open the door to a renewed role for the agency in post-war Iraq.
The United States is expanding its own team to hunt for Saddam Hussein's alleged arsenal of weapons of mass destruction and wants to exclude the IAEA and other U.N. arms inspectors.
The failure of the United States and Britain to find any banned weapons since their March 20 invasion has raised questions about whether the intelligence that helped lead to the war was inaccurate or overplayed to generate support for an invasion.
The director of the Defense Intelligence Agency, Vice Adm. Lowell Jacoby, acknowledged last week that he had no hard evidence of Iraqi chemical weapons last fall but did believe Iraq had a program to produce them.
Secretary of State Colin Powell said parts of the DIA report were taken out of context in news reports.
"The sentence that has gotten all of the attention, in this two-page, unclassified summary, talked about not having the evidence of current facilities and current stockpiling," he said in a broadcast interview.
"The very next sentence says that it had information that weapons had been dispersed to units. Chemical weapons had been dispersed to units."
Because Iraq concealed its banned weapons so well, it will take time to find them, Powell said. But he said, "I'm sure more evidence and more proof will come forward as we go down this road."
Powell said his prewar statement to the United Nations — that there was no doubt Saddam was capable of producing and using such weapons — had been vetted for days by intelligence analysts. "We spent four days and nights out at the CIA, making sure that whatever I said was supported by our intelligence holdings," he said.
Rice said the justification for war was grounded in reams of information from the CIA, intelligence reports from abroad, material from U.N. weapons inspectors and efforts by Saddam's government to conceal what it was doing.
She also pointed to then-President Clinton's statement on Dec. 16, 1998, to explain missile strikes he ordered against military and security targets in Iraq. "I have no doubt today, that left unchecked, Saddam Hussein will use these terrible weapons again," Clinton said.
"No one ever said that we knew precisely where all of these agents were, where they were stored," Rice said in another televised interview.
But she acknowledged that President Bush erred when he spoke in his State of the Union address about how the British government had learned that Iraq had sought uranium from Africa to build weapons.
"We did not know at the time — maybe someone knew down in the bowels of the agency — but no one in our circles knew that there were doubts and suspicions that this might be a forgery. Of course, it was information that was mistaken," Rice said.
Rep. Dick Gephardt of Missouri, a Democratic presidential candidate, said he thought the weapons would be found. But he added if Mr. Bush, the United Nations and world leaders were "all duped, or if they didn't have the right information, then this is the most colossal hype that ever was."
Sen. Pat Roberts, R-Kan., chairman of the Senate Intelligence Committee, said a congressional investigation of how intelligence was used in the run-up to the war is premature. "There's a little tad bit of politics being played here," he said. "I think it's very, very counterproductive."