He is a member of the elite of the elite, not merely one of the 795 super-delegates who could decide the outcome of this race, but a mega-delegate who could shape the views of the others.

In a contest that cries out for a big name such as his to tip the balance in the direction of one candidate or another, Mr Edwards is not alone in remaining quietly on the sidelines.

The Democratic party leadership on Capitol Hill - Nancy Pelosi, the House Speaker, and Harry Reid, the Senate Majority Leader - have been similarly stubborn in their neutrality.

Ms Pelosi is said to be leaning towards Mr Obama and has declared that it would be harmful to the party if the super-delegates overturned the will of voters.

This is seen as code for saying Mr Obama - who has an all-but insurmountable lead among elected delegates - should be handed the nomination.

But she has been more reticent on the subject since a group of wealthy, Clinton-supporting Democratic donors pointed out that what she said contradicted the entire purpose of super-delegates as a fail-safe mechanism for preventing voters from picking an unelectable candidate.

Ms Pelosi now says that as chairwoman of the Convention in August it is important to let the campaigns "work their way through this".

Mr Reid agrees that the party should wait until the final primaries in South Dakota and Montana have taken place on June 3 before annointing a nominee. "It will end pretty soon after that," he said in an interview published yesterday.

Significantly for a man whose son was chairman of the campaign for Mrs Clinton in Nevada, he takes the opposite view to Ms Pelosi about whether super-delegates can overturn the results of Democratic primaries and caucuses.

"They have the opportunity, the ability and the right to vote for whoever they want and I think that's what they should do," he said.

Howard Dean, the chairman of the Democratic National Committee, is being criticised in some quarters for messing up the decision to ban delegates from the potentially critical states of Florida and Michigan.

Asked whether super-delegates should overturn the will of voters Mr Dean suggested that if the race is still close "they will do what they want anyway". But he then rather spoilt this moment of clarity by saying that such a scenario was highly unlikely.

He also dismissed the idea of a Democratic elder intervening to stop a fight, which many believe is damaging the party. As a failed candidate himself in 2004 he added: "Only you know when it's time to leave."

Al Gore, the former Vice-President whose stature has soared since losing the 2000 election to George Bush, said yesterday: "I haven't ruled out making an endorsement, but I haven't been moved to do so. They both have strengths and I'm simply listening and watching like a lot of people."

Tad Devine, a Democratic consultant who advised John Kerry in 2004 but who is unaffiliated this year, suggested that it would be the remaining 250 or so uncommitted super-delegates who would decide the race.

"There isn't any one person, a heavy, a single individual who can come in and put an end to this process," Mr Devine said. "That's not Al Gore. That's not Nancy Pelosi. They are not in a position to wave a magic wand. There will be nobody who is above it all to say the time has come to end the race."

As Mr Gore is reported to have told friends recently: "No one wants to be an umpire."