US President George W. Bush has offered a shifting rationale for the Iraq war - that Saddam Hussein had the capacity to develop unconventional arms if not the actual weapons.
Iraq's weapons of mass destruction was the main reason cited by Bush for the war, in which more than 500 U.S. troops and thousands of Iraqis have died, though no such arms were found and weapons hunters say pre-war intelligence was flawed.
Bush addressed the criticism on Iraq and his handling of the US economy in an appearance on NBC's "Meet the Press" as his job approval ratings continue to slide and some polls show Democratic presidential contender John Kerry could beat him in the November election.
The president defended putting off the results of a bipartisan investigation of Iraq intelligence until March 31, 2005, well after the election, and he stopped short of saying he would testify before it, saying only he would be glad to "visit with them," share knowledge and make recommendations.
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 promised weapons is turning into a credibility problem for the president. A Time/CNN poll released on Sunday said 55 percent of Americans have "doubts and reservations" about Bush and less than half, 44 percent, 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 and 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-September 11, 2001, world.