obama_mccain_5.jpgWASHINGTON (AP) _ The battle for the U.S. presidency has entered its final hours, with polls showing Barack Obama holding a solid lead in his historic quest to become the U.S.'s first black president while rival John McCain grasped for a last-minute upset.

On the last day of his 21-month campaign for the White House, Obama told supporters in Jacksonville, Florida that the outcome of the longest, most expensive U.S. presidential contest in history was up to them.

“That's how we're gonna change this country _ with your help,'' he told the crowd, amid chants of “O-bam-a, O-bam-a.''

“And that's why we can't afford to slow down, sit back, or let up, one minute, or one second in the next twenty-four hours. Not one minute. Not one hour. Not one second. Not now. Not when so much is at stake.''

McCain meanwhile was racing through seven states in a last campaign swing that ended Tuesday morning, in a bid to persuade undecided voters that he, not his rival, was more qualified to lead the U.S.

“With this kind of enthusiasm, this kind of intensity we will win Florida and we will win the election,'' McCain told a relatively modest crowd in Florida.

Looking, again, to distance himself from the unpopular incumbent, President George W. Bush, McCain stressed that he, too, opposes the Republican president's economic policies. But he insisted that Obama could be counted on to raise taxes, something he would not do.

Some polls showed tightening races in Florida, Ohio and a number of battleground states, as the Republicans hammered away at Obama as a tax-and-spend Democrat _ historically, the Republicans' most potent weapon in U.S. presidential contests. They launched a last-minute advertising effort hoping to turn the Democratic tide.

But some national polls suggested Obama's lead was widening overall as the candidates moved to the final stages of the race, with the Democrat leading in Pennsylvania and other states McCain must win to have a chance of capturing the presidency.

A USA Today/Gallup poll published Monday found likely voters favoring Obama by 11 points over McCain, 53-42 percent. The poll was conducted Friday through Sunday among 3,050 adults, and had a margin of error of 2 percent. Other polls showed Obama with a 7 or 8 percentage point lead.

With the economy in trouble and Bush's approval ratings at near-record lows, polls suggest Democrats will not just capture the White House, but expand their majorities in both chambers of Congress. In Florida Monday, Obama once again called the 72-year-old McCain Bush's “sidekick.''

Determined to make sure that partisans translate their support into votes, both campaigns were shifting focus on Monday to get-out-the-vote efforts.

But a large part of the electorate has already rendered their verdict.

A record 27 million votes cast absentee or early ballots in 30 states as of Saturday night. Democrats outnumbered Republicans in pre-Election Day voting in key states.

Obama, 47, a first-term senator from Illinois, appealed to voters frustrated with wars abroad and economic turmoil at home.

He benefited from a campaign that raised hundreds of millions more than his opponent, and capitalized on a U.S. demographic shift as more young and nonwhite voters enter the electorate.

The Republicans have tried to curtail Obama's surge, dubbing him too inexperienced, too liberal and too tainted by associations with the political left to craft the kind of change needed in the country.

McCain's vice presidential running mate, Alaska Gov. Sarah Palin, seized on the taxation issue in her final day of campaigning in Ohio.

While promising that she and McCain would lower taxes, balance the budget and eliminate the U.S. $10 trillion budget deficit, she said Obama had an ideological commitment to higher taxes and had consistently chosen “the side of bigger, more controlling government.''

“We will win! We will win!'' the crowd chanted.

While McCain's message appealed to core Republican voters, it may have failed to win many Democrats and independents in crucial states, where U.S. elections are decided.

To win, a candidate must win at least 270 of the 538 electoral votes distributed to states roughly in proportion to their population.

In most cases, the candidate who wins a plurality of votes in a state wins all of that state's electoral votes.

Obama is favored to win all the states Democrats captured in 2004, when Bush defeated the Democratic Sen. John Kerry. That would give him 251 votes.

He is leading or tied in several states won by Bush, giving him several paths to the 270 vote threshold _ such as with victories in Ohio or Florida, or in a combination of smaller states.

Obama campaign manager David Plouffe said Sunday that the Democrat has spread his bets by aggressively campaigning in traditional Republican states. “We wanted a lot of different ways to win this election,'' he said on Fox television.

McCain, meanwhile, must hold onto as many Bush states as possible and try to capture some major Democratic strongholds, such as Pennsylvania.

McCain campaigned in Florida Monday, and planned stops to Tennessee, Indiana, New Mexico and Nevada before returning early Tuesday to his home state of Arizona.

After Florida, Obama planned appearances in North Carolina and Virginia.

While the polls favor Obama, there are still many uncertainties about how the unprecedented contest will play out.

McCain's advisers said he has come from behind before, most recently to win the Republican nomination. No one is certain, meanwhile, how white Democratic voters in the end will react to Obama's race.

The two candidates have amassed a stratospheric $1 billion, with Obama's campaign raising hundreds of millions of dollars more than his rival.

But McCain's party splurged in the campaign's final days and now are matching or exceeding Obama's advertising blitz in key states.

The Republicans launched a barrage of phone calls to voters in battleground states that featured Hillary Rodham Clinton's criticism of Obama in the Democratic primary.

The Pennsylvania Republican Party also unveiled a TV ad featuring Obama's former pastor, the Rev. Jeremiah Wright, declaring “God damn America!'' in a sermon.

During the primaries, Obama was forced to distance himself from Wright, but McCain said he would not make the pastor an issue in the general election.