National polls and those taken in battleground states show the bitter political rivals in a virtual tie less than 24 hours before Americans choose their leader for the next four years.
Both planned exhausting campaign marathons to key swing states during the final run-up to election day.
Bush began a 16-hour sweep through Ohio, Pennsylvania, Wisconsin, Iowa and New Mexico before ending the day with a rally in Texas.
Kerry planned his own 16-hour extravaganza, rolling through Florida, Wisconsin, Michigan and Ohio, then doubling back for second stops in Ohio and Wisconsin.
Americans will also decide which party holds power in Congress and vote on governorships in 11 states on Tuesday, with Bush's Republicans favoured to retain control of both the Senate and the House of Representatives.
More than 100 million Americans - perhaps as many as 125 million - are expected to cast ballots. The size of the turnout could be critical in determining which candidate gets the 270 electoral votes needed to win, and has made an unpredictable race even harder to forecast.
Before they entrust the campaign to get-out-the-vote efforts on Tuesday, both candidates planned a final day of rallies to fire up supporters and reach out to the small band of undecided voters - as low as 2 to 3% in some polls - that could decide the race.
Both candidates are campaigning
hard in a last bid to boost support
Speaking at Pittsburgh International Airport before a rally in Burgettstown, Pennsylvania, Bush said he was "energised" in the marathon stretch to the finish.
"I'm confident we're going to win," said the president, adding: "The finish line is in sight and I just want to assure you I've got the energy and the optimism and the enthusiasm to cross the line."
Security heads agenda
In a bitter race dominated by the Iraq war and national security, Kerry once again tried to squash criticism he would be soft on security issues if he were elected president.
"The Republicans are trafficking in fear because they haven't delivered to America the security that we deserve," said Kerry in an interview aired by CBS. "I will do a better job than George Bush at making America safe."
Several new polls showed the race was a statistical dead heat and polls in the approximately 10 battleground states that will decide the election were also close.
"The Republicans are trafficking in fear because they haven't delivered to America the security that we deserve"
Democratic candidate John Kerry
Bush led Kerry 48% to 47% in the latest Reuters/Zogby three-day national tracking poll on Monday, well within the margin of error.
However, Kerry was favoured by young voters - those between the ages of 18 and 29 - by 64% to 35% - but the size of the turnout in that voting bloc is one of the biggest unknowns of Tuesday's election.
The national poll indicated independent candidate Ralph Nader, blamed by some Democrats for drawing enough votes from former vice-president Al Gore to cost him the election in 2000, with 1.2%.
As the race entered its final hours, an election watchdog reported complaints of irregularities.
Officials reported record levels of early voting across the country, including nearly two million voters in Florida. The watchdog group Common Cause, which set up a hotline to record complaints about voting problems, said it had received more than 53,000 calls nationally.
Also in Florida, a sheriff's deputy tackled, punched and arrested a US journalist for taking pictures of people waiting in line to cast early ballots in West Palm Beach, local media reported.
One watchdog has received
53,000 calls on voting problems
A sheriff's spokesman said later the deputy was enforcing a new, unannounced county rule prohibiting reporters from interviewing or photographing voters lined up outside the polls, the Palm Beach Post said.
The deputy tried to grab the camera of James Henry, a freelance journalist who has written for The New York Times and The Washington Post.