Mr Latham said the government had claimed Australia had to go to war to find and destroy Iraq's weapons of mass destruction.
'It was a war justified primarily to find and eliminate weapons of mass destruction. None were used in the conflict, none have been found since,' Mr Latham told Sydney radio 2UE.
'I think they made a mistake in going to a war on Iraq, whatever the reason or motivation was, I think it was a mistake.
'And on that basis it is a worry it was a war that was sustained on a premise that hasn't been proven and hasn't been justified.
'And for that reason you'd have to be worried about the conduct of Australian foreign policy.'
Mr Latham said Australia had to have very good reasons to go to war.
'We shouldn't be getting into overseas conflicts unless we've got the very best reason to do so,' he said.
In a rebuff to the close links between the government and the Bush administration, Mr Latham said a Labor government would act independently on issues ranging from Iraq to the proposed free trade agreement.
'We value the American alliance, but we value more the Australian national interest, and if there is a point of disagreement, of course we will stand up for what's best for this country,' he said.
The comments were immediately attacked by Acting Prime Minister John Anderson, who accused Mr Latham of defending the regime of Saddam Hussein and of other rogue states.
Howard is running for re-election without any real program by talking about national security and (so far) not much else. The increasing holes in the WMD story cannot be good news for him, especially after Blair's weekend admissions (blogged below) and now the O'Neill allegations. A Man of Steel who was sold a pup badly needs something else to talk about.
The attacks on Latham right after his election died away on the release of polling that all states except Queensland and all age groups agreed with his characterisation of Bush as the 'worst and most incompetent president'. The new information about Bush's governance cannot add much to Howard's own reputation as a shrewd operator. And shrewdness is all he has ever really offered.