WASHINGTON, US - DEMOCRAT Hillary Clinton charged the Iraq war may end up costing Americans US$1 trillion (S$1.4 trillion) and further strain the economy, as she made her case for a prompt United States troop pullout from a war 'we cannot win'.

This week marks the fifth anniversary of the US invasion of Iraq, but voters now say the economy is their top issue in the campaign for the November presidential election.

Mrs Clinton, the former first lady who is trying to convince voters she has foreign policy gravitas, on Monday hurled criticism both at her rival for the Democratic presidential nomination, Illinois Senator Barack Obama, and the Republicans' choice, Arizona Senator John McCain.

She said the war has sapped US military and economic strength, damaged US national security, taken the lives of nearly 4,000 Americans and left thousands wounded.

'Our economic security is at stake,' she said. 'Taking into consideration the long-term costs of replacing equipment and providing medical care for troops and survivors' benefits for their families, the war in Iraq could ultimately cost well over US$1 trillion.' It has already cost US$500 billion.

New York Senator Clinton pointedly noted that while Mr Obama insists he will withdraw US troops in Iraq within 16 months of taking office, his former foreign policy adviser, Ms Samantha Power, had said he might not follow through on the pledge.

'In uncertain times, we cannot afford uncertain leadership,' Mrs Clinton said. Ms Power resigned after a British newspaper quoted her as calling Mrs Clinton a 'monster'.

Mr Obama, who routinely scolds Mrs Clinton for having voted for a 2002 Senate resolution that authorised the war, fired back.

'I think Senator Clinton has a lot of chutzpah, as they say, to in some way to suggest that I'm the person who has not been clear about my positions on Iraq. I have been opposed to this war from the start,' he told PBS.

Mr Obama, who leads Mrs Clinton in nominating delegates with the next important contest in Pennsylvania not until April 22, began a second straight week on the defensive.

A CNN/Opinion Research poll said 52 per cent of Democrats would most like to see Mr Obama as the party's nominee, compared to 45 per cent for Mrs Clinton. Mrs Clinton had led on the same question 49 per cent to 46 per cent in early February.

Mr Obama, who would be the first United States black president, was due to deliver a speech about race on Tuesday in Philadelphia to try to put to rest questions about his Chicago preacher, Mr Jeremiah Wright, an African-American who sometimes laces his sermons with anti-American rhetoric.

Race speech

'I am going to be talking about not just Reverend Wright, but the larger issue of race in this campaign,' he said.

Mr McCain, who has clinched the Republican presidential nomination, drew fire from Mrs Clinton even as visited Iraq as part of a Middle East and Europe swing this week that he hopes will remind Americans of his national security credentials.

She accused Mr McCain of joining President George W. Bush in pushing a 'stay the course' policy that would keep US troops in Iraq for 100 years.

'They both want to keep us tied to another country's civil war, a war we cannot win,' she said. 'That in a nutshell is the Bush/McCain Iraq policy. Don't learn from your mistakes, repeat them.'

Mrs Clinton said if elected she would convene military advisors and ask them to develop a plan to begin bringing US troops home within 60 days of taking office next January.

Mr McCain is a big backer of Mr Bush's troop build-up in Iraq, credited for slowing the death toll there. He told CNN if Mrs Clinton started bringing home troops, 'Al-Qaeda wins'.

Added McCain spokesman Jill Hazelbaker: 'It would be the height of irresponsibility to stick with campaign promises to the left wing of the Democratic Party and proceed with withdrawal regardless of what the situation is on the ground in Iraq in January 2009.'

Mr McCain appears to be benefiting from the protracted Democratic battle. Polls show him running slightly ahead or nearly even with both Mr Obama and Mrs Clinton in hypothetical matchups for the November election. -- REUTERS