Senator Obama is favoured over Mrs Clinton on Tuesday in Virginia, Maryland and the District of Columbia, the latest battlegrounds in a tight back-and-forth struggle between the two candidates for the Democratic nomination in November's election.

At stake in Tuesday's voting are 168 pledged delegates to this summer's nominating conventions. Polls close at 7 pm EST/ (8am Wednesday Singapore time) in Virginia and at 8 pm EST/ (9am Singapore time) in Maryland and the District.

The contenders crisscrossed the area around the nation's capital on Monday, hunting for support in a presidential race where momentum has been difficult to sustain.

Senator Obama swept four contests over the weekend in the states of Maine, Louisiana, Nebraska and Washington, extending a slight lead in the battle for pledged delegates who select the nominee.

Senator Obama, an Illinois senator, now has 943 pledged delegates to Mrs Clinton's 895, according to a count by MSNBC - well short of the 2,025 needed to clinch the Democratic nomination.

Mrs Clinton, a New York senator, shook up her campaign staff on Sunday, replacing campaign manager Patty Solis Doyle with longtime aide Maggie Williams. But she voiced confidence about her campaign's future.

'If you look at the states that are upcoming I'm very confident,' Mrs Clinton told reporters at a General Motors plant in White Marsh, Maryland, near Baltimore. 'This is an ongoing contest and I feel very good about it.'

But Mrs Clinton was already looking past the three contests on Tuesday and next week's battles in Wisconsin and Hawaii - all of which favour Senator Obama - to focus instead on crucial March 4 contests in the big states of Texas and Ohio.

'I am absolutely looking to Ohio and Texas because we know that those are states where they represent the broad electorate in this country,' Mrs Clinton said.

'They represent the kind of voters that will have to be convinced and won over in the general election.'

The two candidates agreed to another one-on-one debate in Austin, Texas, on Feb 21, two days after the Wisconsin and Hawaii contests. They will also meet in a Cleveland, Ohio, debate on Feb 26.

No meeting with Edwards
Senator Obama's planned meeting with former North Carolina Senator John Edwards, who recently dropped his presidential bid but has not made an endorsement, was postponed.

Senator Obama said it would be rescheduled.

'We're gonna make it happen,' he told reporters during a stop at a coffee shop in Silver Spring, Maryland, in the suburbs of Washington.

Mrs Clinton wooed Mr Edwards on Thursday in North Carolina.

She argued she had the best chance of beating Republican front-runner John McCain, an Arizona senator who has all but clinched the nomination but lost two of three contests over the weekend to former Arkansas Governor Mike Huckabee.

'We have to start imagining right now what it will take for our nominee to go toe-to-toe with John McCain on national security, on defence, on homeland security,' she said. 'I feel totally comfortable standing up there with John McCain.'

Clinton strategist Mark Penn said in a memo the former US first lady would be better able to withstand Republican attacks in a general election, having faced them for years.

Mrs Clinton echoed the theme in an interview with a local Washington television station. 'I have been vetted, I have been through this. There isn't any new information,' she said. 'I don't think you can say that about my opponent.'

Senator Obama, in a later interview with the same station, said he did not buy the argument. 'What we have shown is that we can take a punch,' he said. 'We have shown we can take a loss.'

Mr McCain still faces opposition from Republican conservatives unhappy with his views on immigration and other issues. But he has won more than 700 of the 1,191 delegates needed for nomination - an overwhelming lead on Mr Huckabee, who has barely more than 200.

At a Monday night rally in Richmond, Mr McCain was joined by two conservative Republican former Virginia governors - James Gilmore and George Allen - and Christian conservative leader Gary Bauer, who endorsed Mr McCain.

Mr McCain also notified the Federal Election Commission he would not take public matching funds during the nominating process - avoiding federal spending limits and allowing him to raise and spend more money as he prepares for November's general election.

He had told the FEC he would take the funds last summer when his campaign was nearly broke and hitting bottom, but the money would not have been available until next month and he would have been limited to spending about US$54 million (S$77 million) before the September convention.

Asked why he changed his mind on the money, he said: 'Didn't need to. That was my thinking, we didn't need to.' -- REUTERS