By Richard Allen Greene BBC News, Washington

While US presidential elections normally start with a trickle of states choosing their preferred candidates one by one, next year could see up to half the states in the country making their choices on one day.

Voters in early-primary states often meet candidates in person

The US has had "Super Tuesdays" in the past - days when as many as eight or nine states all held their primary elections on the same day, sometimes effectively choosing the two candidates for president at a stroke.

But it has never seen anything like what is shaping up for 5 February 2008 - which some wits are calling "Super Duper Tuesday".

The nation's most populous state, California, has moved its presidential primary to that date, as have other heavyweights such as New York and New Jersey, as well as Georgia.

Illinois and Colorado are only a governor's signature away from joining them on that date.

Florida has decided to go even earlier, on 29 January, risking punishment by the national parties.

'Pure self-interest'

The race to have primaries earlier and earlier is a frantic effort to have a greater role in choosing the two candidates for president, political scientist Larry Sabato says.

"States have gradually awakened to the fact that if you can be in on the process early, you can have special influence in choosing the two nominees - one of whom will be president and will be indebted to you," says Mr Sabato, director of the Center for Politics at the University of Virginia.

"It's pure self-interest."

Anyone who says they know what effect this will have is just guessing Larry Sabato, University of Virginia Center for Politics

For the past several decades, states have held their primary elections (or caucuses, a slightly different method of choosing a candidate) throughout the spring and summer of presidential election years, leading up to national party conventions at which a candidate is officially selected.

Candidates who do not do well in the early primaries tend to drop out, making the official nomination at the convention something of a formality - or coronation.

Thus, states with early primaries have disproportionate influence over who the candidates are.

Mr Sabato says there is no way to predict which candidates will benefit from what could effectively be a coast-to-coast primary on 5 February 2008.

"Anyone who says they know what effect this will have is just guessing. They may be educated guesses, but they are just guessing."

First in the nation

Amid all the uncertainty, there is no need for guesswork about which state will actually hold its primary first.

Campaigning can be very personal in New Hampshire

Tiny New Hampshire jealously guards its "first-in-the-nation primary" status.

For decades, candidate after candidate has made pilgrimages to meet potential voters in coffee shops, hardware stores and county fairs - in a state with a population comparable to that of Glasgow, Frankfurt, or Memphis, Tennessee.

Local law allows the secretary of state to set the date of the New Hampshire primary at his sole discretion at a very late date - making it all but impossible for another state to jump the queue.

William Gardner has been the man setting New Hampshire primary dates for the past 31 years.

He has not yet decided when New Hampshire's 2008 primary will be - but he says it could take place before 2008 even begins.

You could sweep the whole thing before anyone figured out what happened Dante Scala, author State profile: New Hampshire

"It could be this year," he told the BBC.

"I have not yet decided when I will set the date," he says, adding that once he does so, it does not take "as long as one might think" to put the machinery in place for casting ballots.

'Perverse effect'

Mr Gardner is not especially concerned by the states racing to have their primaries earlier in the cycle.

Mr Gardner wields significant power over White House ambitions

California has been jockeying for influence proportional to its size for at least a decade, he observes.

"They moved their primary from June to the end of March for 1996. That didn't accomplish what they were hoping, so they moved up to the first week in March - and that didn't accomplish what they were hoping so they are trying again."

A few other small or medium-sized states will be holding their primaries before 5 February, either by tradition or with the permission of the national parties.

And many experts think those states will become even more important - not less so - with so many states voting on one day soon afterwards. "Front-loading will probably have the perverse effect of making New Hampshire even more important," says Dante Scala, author of Stormy Weather: The New Hampshire Primary and Presidential Politics.

"Let's say Barack Obama beats Hillary Clinton in Iowa and New Hampshire," he says - underlining that he is not making predictions.

"Hillary will still have a lot of money to compete on 5 February, but precious little time to recover.

"The newspapers will be trumpeting that Obama won, and that will be the first time many voters hear of the primary process.

"Because of the compression of the calendar, you can't afford to stumble early," he warns.

"You could sweep the whole thing before anyone figured out what happened."

Voters 'left out'

That is exactly what worries William Galvin, the secretary of state of Massachusetts, who has studied the issue for the National Association of Secretaries of State.

"The people who are being left out of this are the voters, especially those who aren't active in party affairs," he says.

"There won't be enough time for voters to focus on these candidates."

The association has been promoting an alternative system where four regional primaries would be held over the course of four months, but has made little headway since the plan was devised after the 2000 election.

Mr Galvin says the problems that prompted the association to draft the plan "have gotten much worse" since then.

If the 2008 cycle is "enough of a debacle, you're going to see Congress step in", he predicts.