Bush conceded that it was "correct" that weapons of mass destruction had not been found in Iraq but emphasised a different reason why the war was necessary.
"He had the capacity to have a weapon, make a weapon. We thought he had weapons. The international community thought he had weapons. But he had the capacity to make a weapon and then let that weapon fall into the hands of a shadowy terrorist network," Bush said.
The failure to find the alleged weapons is turning into a credibility problem for the president. A Time/CNN poll released on Sunday said 55 per cent of Americans have "doubts and reservations" about Bush and fewer than half, 44 per cent, said he is a leader they can trust.
Bush decided on his own to make a rare appearance on the top-rated Sunday talk show in an attempt to regain the high ground of the election-year Iraq debate, aides said.
They concede Bush is going through a tough period and believe his tumbling poll numbers are in part a result of a chorus of attacks by Democratic challengers. The interview is part of an aggressive push to answer the critics.
With more than 500 Americans killed during the war and its chaotic aftermath, Bush said he did not believe they died in vain.
"Saddam Hussein was dangerous," he said.
Bush and his team had said in the run-up to the war that it was necessary to topple Saddam because he had stockpiles of chemical and biological weapons, was trying to build a nuclear weapon and represented a grave danger in the post-Sept. 11, 2001, world.
Democratic front-runner Kerry wasted no time in criticising Bush for offering a new war rationale.
With no weapons found in Iraq, the administration had previously justified the war by arguing Saddam was worth toppling because of his appalling human rights record.
In the interview, Bush was read a quote by Deputy Defence Secretary Paul Wolfowitz who said this was not a justification for attacking Iraq. He declined to address it.
"Now the president is giving us a new reason for sending people to war, and the problem is not just that he is changing his story now, it is that it appears he was telling the American people stories in 2002," Kerry said in Richmond, Virginia.
He called on Bush to allow a "legitimate and immediate investigation into the extraordinary failure" of US intelligence or whether the Bush administration hyped the threat for political purposes.
Last Friday Bush appointed a bipartisan commission to investigate flaws in intelligence used to justify the war based on former chief weapons hunter David Kay's fruitless search.
Bush said he gave the commission until March 2005 to report back because he did not want its work to be hurried and that voters will have ample time to assess "whether or not I made the right decision" in invading Iraq.
"It's important that this investigation take its time," he said.
Bush said CIA Director George Tenet's job was not in jeopardy but he blamed the intelligence he received for his pre-war convictions that Iraq was a danger.
"I expected to find the weapons ... 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 were valid," he said.
On "Fox News Sunday," Sen. John Edwards of North Carolina said the commission should fully investigate but he hoped it could finish before the election.
"It does bother me" that the commission is not slated to complete work until March 2005," he said. But, "The commission needs to conduct its study in a serious way. It shouldn't be politically motivated or politically driven. We need to get to the bottom of this."
What Bush has said previously
Here are some of President George W. Bush's comments on weapons of mass destruction in Iraq.
2002:
BUSH OUTLINES 'IRAQI THREAT,' Oct. 7:
"The Iraqi regime ... possesses and produces chemical and biological weapons. It is seeking nuclear weapons."
2003:
BUSH MAKES THE CASE AGAINST IRAQ, March 17:
"Intelligence gathered by this and other governments leaves no doubt that the Iraq regime continues to possess and conceal some of the most lethal weapons ever devised."
BUSH TELEVISION INTERVIEW ABOUT WEAPONS, APRIL 24:
The United States is learning in interrogations and interviews with Iraqi scientists that "perhaps he (Saddam) destroyed some, perhaps he dispersed some" and that "it's going to take time to find them."
AFTER TALKS WITH RUSSIAN PRESIDENT VLADIMIR PUTIN, June 2:
"We've discovered a weapons system -- biological labs that Iraq denied she had and labs that were prohibited under the UN resolutions."
BUSH IN A TELEVISED SPEECH TO THE NATION, SEPT 7:
"We acted in Iraq, where the former regime sponsored terror, possessed and used weapons of mass destruction, and for 12 years defied the clear demands of the United Nations Security Council..."
2004:
BUSH'S STATE OF THE UNION ADDRESS, Jan 20:
"Had we failed to act, the dictator's weapons of mass destruction programmes would continue to this day."
DURING TALKS WITH POLISH PRESIDENT KWASNIEWSKI, Jan 27:
"First of all I think it's very important for us to let the Iraq Survey Group do its work so we can find out the facts, compare the facts to what was thought."
"There is no doubt in my mind that Saddam Hussein was a grave and gathering threat to America and the world. And I say that based upon intelligence that I saw prior to the decision to go into Iraq, and I say that based upon what I know today. And the world is better off without him."
PRIOR TO BUSH MEETING WITH HIS CABINET, Feb 2:
"What we don't know yet is what we thought, and what the Iraqi Survey Group has found, and we want to look at that."
BUSH INTERVIEW WITH NBC, Feb 8:
"I think, if I might remind you that in my language I called it a grave and gathering threat, but I don't want to get into word contests. But what I do want to share with you is my sentiment at the time. There was no doubt in my mind that Saddam Hussein was a danger to America," Bush said.
"Well, because he had the capacity to have a weapon, make a weapon. We thought he had weapons. The international community thought he had weapons. But he had the capacity to make a weapon and then let that weapon fall into the hands of a shadowy terrorist network," Bush added.
- REUTERS
Transcript from NBC television programme Meet the Press:
Interview with George W Bush
Herald Feature: Iraq
Iraq links and resources
Herald Feature: US Election
Related information and links
