He said he had not called Saddam Hussein an "imminent threat" but said it would have been too late if the US had waited until the danger was that close.
"I'm a war president. I make decisions here in the Oval Office in foreign policy matters with war on my mind," he said.
"I see dangers that exist and it's important for us to deal with them."
He defended the intelligence that indicated Iraq had or was developing weapons of mass destruction.
"The evidence I had was the best possible evidence that he had a weapon," he said.
Challenged by interviewer, Tim Russert, that no weapon had been found, Mr Bush replied: "What wasn't wrong was the fact that he had the ability to make a weapon."
The president said the arms could have been destroyed, moved or hidden.
In North Korea, for example, he said "the diplomacy is just beginning".
He stressed the US public would have plenty of time to judge his role, though the intelligence commission will not report until March 2005, months after the presidential election.
A British inquiry into the pre-war intelligence is expected to report this summer but Mr Bush defended the 14 months he is allowing for findings, saying it should not be "hurried".
When it does come time to vote in November, he said he thought the biggest issue would be "who can properly use American power in a way to make the world a better place".
He acknowledged that the economy was also important, and said it was strong despite a record deficit.
"It's important for people who watch the expenditures side of the equation to understand we are at war," he said.
"They're just wrong. There may be no evidence, but I did report; otherwise I wouldn't have been honourably discharged," he said.