Although turnout among ordinary Democratic voters has been high, neither Mrs Clinton nor Mr Obama is expected to garner the 2,025 normal delegates they need by the time state caucuses and primaries are complete on June 7.

So, unless the two contenders broker some kind of deal, they will be left at the mercy of 795 super- delegates chosen on the basis of their status as current or former elected office-holders and party officials.

To give a measure of their power, 370 regular delegates in California were allotted based on the votes of more than 4.5 million people in the state's Feb 5 primary.

That means each of California's 66 super-delegates will cast a convention ballot equivalent to a regular delegate picked by more than 12,000 primary voters.

In addition, and unlike normal delegates, these super-delegates are free to make up their own minds rather than following the will of the people.

Mrs Clinton currently enjoys a lead of close to 80 super-delegates, but about 300 have yet to choose which candidate to support.

And the amount of power they wield means they are enjoying almost as much, if not more, attention from the campaign camps as, say, Wyoming, where caucuses on March 8 will choose a mere eight delegates.

Philadelphia super-delegate Carol Ann Campbell demonstrated the lengths to which the two camps are going by playing a recent voicemail message from Mr Obama's wife Michelle.

'Hi, Carol, this is Michelle Obama,' the message goes.

'I'm the wife of Barack Obama, who is running for president.

'Your primary is coming up soon and we hope to do well there, but we want people on board who are supportive as soon as possible.'

Similarly, fellow super-delegate Debbie Marquez describes receiving a telephone call at home from former president Bill Clinton - himself a super-delegate - who then attempted to persuade her to back his wife.

Mr Clinton's call was in vain, however, as Ms Marquez is backing Mr Obama. She added that nothing Mr Clinton said persuaded her to jump ship.

For her, the fact that her state, Colorado, backed Mr Obama by about 2-1 in its Feb 5 contest is of overriding importance.

But that is not a universal view, and the Clinton and Obama camps are increasingly moving away from arguments over policy towards sniping at each other over whether super-delegates should follow their own beliefs or the will of the people.

With Mr Obama gaining momentum after eight consecutive victories in the nomination race, his backers argue that the super-delegates should reflect this trend, while Mrs Clinton's camp is stressing their independence of choice.

CNN on Sunday quoted Mr Obama's chief political strategist, Mr David Axelrod, as telling CBS: 'Super-delegates does not mean that they should leap over the will of the people in a single bound.'

At the same time, Mrs Clinton's communications director Howard Wolfson told the channel that super-delegates 'are supposed to vote their conscience'.

But the two contenders have not forgotten about the ordinary voter altogether, and Mrs Clinton was yesterday fighting to stave off a wave of momentum for Mr Obama ahead of today's primary contest in Wisconsin.

Mr Obama hopes to extend his winning streak in the Midwestern state, as well as in caucuses in Hawaii.

But polls showed a tight race in Wisconsin, with the Illinois senator enjoying a narrow five-point lead over the former first lady, according to a survey by Research 2000, US media reported.

AGENCE FRANCE-PRESSE, LOS ANGELES TIMES, NEW YORK TIMES