In a rare television interview on Sunday with the American NBC network, Bush said his assertion on 17 March that intelligence leaves no doubt Iraq possesses "some of the most lethal weapons ever devised" was incorrect.
But when challenged by interviewer Tim Russert, the president denied he took the nation to war under false pretenses.
"First of all, I expected to find the weapons," he said. "I based my decision on the best intelligence possible, intelligence that had been gathered over the years, intelligence that not only our analysts thought was valid but analysts from other countries thought was valid.
"And I made a decision based upon that intelligence in the context of the war against terror. In other words, we were attacked, and therefore every threat had to be reanalysed...
'War on terror'
"We remembered the fact that he [Saddam Hussein] had used weapons, which meant he had weapons. We knew the fact that he was paying for suicide bombers. We knew the fact he was funding terrorist groups. In other words, he was a dangerous man."
Bush also attempted to justify the fact that no weapons of mass destruction have been found in Iraq 10 months after America invaded the country.
"I think that when you do hard things, when you ask hard things of people, it can create tensions. I'll tell you, though, I'm not going to change. I won't change my philosophy or my point of view."
President George Bush
He said Iraqi WMDs could have been destroyed during the war, could still be hidden, or could have been transported to another country.
And when asked why people around the world hold him in such contempt, Bush reacted defiantly.
"I think that when you do hard things, when you ask hard things of people, it can create tensions," he said. "I'll tell you, though, I'm not going to change. I won't change my philosophy or my point of view.
"I believe I owe it to the American people to say what I'm going to do and do it, and to speak as clearly as I can, try to articulate as best I can why I make decisions I make, but I'm not going to change because of polls. That's just not my nature."
Bush's appearance was a rare foray for the president into the cut-and-thrust of lengthy television interviews.
It comes as US polls suggest his approval rating has dropped below 50%.
Democrat Senator John Kerry, his likely challenger in the November presidential elections, also has a lead of five to seven points over Bush, according to two recent polls.