Before a packed house at the Kodak Theatre in Los Angeles, Mr Obama and Mrs Clinton used opening remarks to take restrained digs at each other, notably lacking the venom of previous televised exchanges.

Illinois Senator Obama - seeking to emphasise his driving campaign theme of change and a break with previous political eras - described the forthcoming US election as a choice between 'the past and the future.'

Former first lady Clinton meanwhile returned to her theme of experience, stressing the need for the incoming president to be ready to lead from day one.

The two Democratic front-runners also stressed differences of opinion on the issues of Iraq and international diplomacy.

Mrs Clinton took aim at Obama's stated intention to seek talks with the United States traditional foes, most notably Iran.

'I think that we've got to have a full diplomatic effort, but I don't think the president should ... have meetings without preconditions with five of the worst dictators in the world,' Mrs Clinton said.

Mr Obama responded by reminding the audience of his opposition to the war in Iraq, adding that the next president would be required to show 'the kind of judgment that will ensure that we are using our military power wisely.' He also defended his decision to seek talks with Iran.

'I think that, and the national intelligence estimate, the last report suggested, that if we are meeting with them, talking to them, and offering them both carrots and sticks, they are more likely to change their behaviour,' he said.

'And we can do so in a way that does not cost billions of dollars, thousands of lives, and hurt our reputation around the world.' -- AFP