The Republican president and his Democratic rival blitzed battleground states as the hours narrowed to today's election showdown, pitching their plans to win the war on terror and to stabilise Iraq, seeking to sway the undecided voters expected to decide the race.

Bush barnstormed six states yesterday before returning to his Texas ranch. Kerry charged through four states in less than 24 hours.

A high turnout has been predicted for the election, which will decide the presidency and control of Congress.

Late polls gave Bush, 58, a razor-thin nationwide lead but indicated the result in key swing states remained anyone's guess. Both parties are poised for a repeat of the intense legal battle that overshadowed the 2000 election in states where the result could be disputed.

Four of the latest polls suggest a down-to-the-wire photo finish in today's ballot and four others gave the president a statistically insignificant lead of one to three points.

The victor requires a majority of the 538 Electoral College votes that decide the presidency and are awarded in separate, mostly winner-take-all races.

The verdict appeared to hinge on the results in Florida and a handful of northern states such as Pennsylvania and Ohio.

Polls showed Kerry with a slight advantage in Pennsylvania and Bush with a small edge in Ohio, which no Republican has ever lost and still gone on to win the White House. Florida was a complete toss-up.

Voter turnout today could be the key factor, with signs that it may be significantly higher than the 106 million who voted in 2000. The weather also traditionally plays a role.

Analysts have not ruled out a candidate winning the popular vote and losing the election -- as Democrat Al Gore did in 2000 -- or a 269-269 tie in the electoral vote that could force Congress to decide the outcome.

"I expect this election is going to be decided Tuesday night," Kerry told The Associated Press on Sunday, "but, given experience, I would be irresponsible if I wasn't prepared to be able to protect every person's right to vote."

In an interview broadcast yesterday on ABC's "Good Morning America," Kerry predicted "a record turnout" and said he believed "Americans are determined not to see a repeat of 2000." Bush won the presidency in 2000 in a postelection tangle broken when the Supreme Court stopped a Florida recount.

Bush said it was vital to see a clear winner emerge election night, especially considering how closely the process is being watched around the world.

"We'll see how it goes Tuesday night but I really think it's important not to have a world of lawsuits that stop the will of the people from going forward," the president told "Dateline NBC."

The long, bruising campaign was finally ending, surely not a moment too soon for the combatants. Kerry occasionally coughed during his speech at a Tampa rally and Bush stocked up on lozenges and cut down or eliminated caffeine, which constricts the vocal cords.

While the presidential race will be the headline event today, some 156 million registered voters will also decide the composition of Congress, where the Republicans control both houses, 11 governorships and a series of state referenda initiatives.

Meanwhile, thousands of Democratic and Republican party lawyers have already been deployed around the country as charges and allegations fly and vote-related lawsuits are filed.

"The likelihood is that if it's close it will go to the courts, even if there are only one or two states where it's close," said Kevin McMahon, a political science professor at New York University-Fredonia.

Howard Gillman, a specialist on constitutional law and author of a book on the controversial 2000 presidential race between Bush and Democrat Al Gore, agrees.

"Two things make it likely," he told AFP. "The election is still very, very close" and there is "a huge legal infrastructure that the parties have put into place."

Final results in the 2000 presidential race were delayed for 36 days due to disputes over balloting in the southeastern state of Florida, and resolved only after US Supreme Court intervention.

Party officials "are prepared in a way that they were not really prepared last time," said Gillman.

Armies of Republican and Democratic observers have already shown up at early voting sites, and will be out in force on the election day. "Chances are, with all these people on the ground, controversies are going to spark," said McMahon.

Then there are provisional ballots, mandated by the US Congress in 2002 after thousands of mainly African-American Florida voters said they were improperly denied ballots because their names were improperly removed from voter rolls or not on them.

Key details on provisional ballot use however were left up to the states, and many are being litigated.

This year observers largely believe the US Supreme Court will stay out of the electoral melee. The court "would be extremely hesitant to get involved again," McMahon said, "unless there is some gross abuse at the state level."

Most observers hope that whoever wins will do so by a convincing margin, noting that in some states election lawsuits are forbidden if the difference between the candidates is more than one percent.

If not, the consequences could be far reaching, said University of Maryland political science professor Mark Graber.

"It was a semi stolen election last time," Graber said, referring to the 2000 presidential election. "If there are two in a row, there will be enormous damage."

"(If) people increasingly think the regime is not legitimate it might lead to some instability," he said.

(AFP/AP/REUTERS/WASHINGTON POST)