Four states were holding presidential primaries or caucuses for either the Democratic or Republican nomination in the first votes since the Super Tuesday contests ended in a stalemate for Clinton and Obama.

Around 200 delegates to the Democratic party's nominating convention are at stake over the weekend, and the biggest prize will be Washington state which has 78 delegates up for grabs.

The caucuses there were set to open at 1pm (2100 GMT).

Both candidates campaigned fiercely in the northwestern state Friday in their monumental battle to represent the Democratic Party in the November election, with Senator Clinton focused on her universal health care plan and Senator Obama pushing his message of change in his bid to be America's first black president.

With no time to stop and pause, Clinton and Obama busily campaigned in Maine early on Saturday, with rallying stops scheduled in Virginia later the day, including an appearance by both at the state Democratic Party's high-profile Jefferson-Jackson dinner in Richmond.

On Tuesday, Virginia, Maryland and Washington, DC will hold primaries on Tuesday with around 200 delegates at stake.

Meanwhile in Louisiana, polls opened at 6am (1100 GMT) for both Republican and Democratic primaries on Saturday.

Democratic caucuses in the midwestern state of Nebraska were set to open at 9am (1500 GMT), while Kansas was to open its Republican caucuses at the same time.

In the northeastern state of Maine, Democrats will also vote on Sunday, where former president Bill Clinton has been trying to whip up support for his wife.

A tally by independent pollsters RealClearPolitics on Saturday put Clinton marginally ahead in the delegate count, with 1,076 to Obama's 1,006 - with half of the final total, or 2,025, necessary to clinch the party's nod.

More than 400 delegates are up for grabs in the seven upcoming votes.

The protracted race is beginning to take its toll, as Clinton, 60, has struggled to match 46-year-old Obama's fundraising in recent days as she bids to be the country's first woman president.

She had to pump some five million dollars (S$7 million) of her own money into the campaign this week.

Republican Senator John McCain, who is virtually guaranteed his party's nomination after former Massachusetts governor Mitt Romney quit the field, got a tacit boost on Friday from President George W. Bush.

Addressing a conference of fervent conservatives doubtful of McCain's own moderate political stances, Mr Bush warned of the high stakes in the 2008 White House race and called on his party to rally around the eventual nominee.

Without naming McCain, who was his rival in the 2000 presidential election, Bush cast the election as a referendum on his own policies such as the Iraq war.

'Prosperity and peace are in the balance,' Mr Bush told supporters.

'So with confidence in our vision and faith in our values, let us go forward, fight for victory, and keep the White House in 2008,' he added.

McCain, 71, a Vietnam war hero, got a mixed reception when he addressed the CPAC conference on Thursday, with catcalls and boos mixed in with cheers.

The maverick Arizona senator has sought to shore up his conservative credentials with the party's base which, despite his solid conservative voting record, has been angered by positions he has taken on illegal immigration and finance reform.

Mr Bush has not yet openly backed a candidate, but says he will get behind the party's choice.

Ordained Baptist preacher and former Arkansas governor Mike Huckabee, who has around one-third the number of delegates as McCain, was endorsed Friday by James Dobson, founder of the influential Focus on the Family evangelical group.

Dobson said Huckabee's 'unwavering positions on the social issues, notably the institution of marriage, the importance of faith and the sanctity of human life, resonate deeply with me and with many others'.

Huckabee, who has been picking up support from the country's rural conservatives, has been tipped as a possible vice-presidential candidate. -- AFP