With President George W. Bush and his Democratic rival John Kerry looking at a photo finish to match the 2000 cliffhanger, both sides have worked hard to register supporters and make sure they get to the polls.

"I think it's basically a question of which one does the organising and gets out his vote because there are virtually no undecided voters any more," said Stephen Hess, a political analyst with the Brookings Institution.

The importance of turnout has been a political cliche in a country where for the last three decades barely half the electorate has bothered to show up to cast their ballo|s for president.

But this year it's a question of basic math in an idiosyncratic system that decides the presidency by electoral votes apportioned out among the states and awarded in separate, mostly winner-take-all contests.

Bush, who lost the popular tally four years ago by more than half a million votes to Democrat Al Gore, won the election by 271 to 266 electors after a bitter recoun| battle in the state of Florida that went to the US Supreme Court.

No less |han 12 states were decided by less |han five percent; five by less than one percent. Florida fell into Bush's column by 537 votes out of six million cast; the western state of Mexico went Democratic by 366 votes.

So the two parties were not only scrambling to boost their numbers nationally, but were targeting key constituencies in 10 so-called battleground states that could put them over the |op in the electoral count.

Some 106 million Americans, 54 percent of those eligible, cast ballots in 2000. Curtis Gans, director of the Committee for the Study of the American Electorate, forecast an additional 12 million to 15 million would vote this time ou|.