WASHINGTON: The battle for the US presidency entered its final hours yesterday, with polls showing Barack Obama holding a solid lead in his historic quest to become the US’ 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 US presidential contest in history was up to them.

“That’s how we’re gonna change this country — with your help,” the Illinois senator 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 24 hours. Not one minute. Not one hour. Not one second. Not now. Not when so much is at stake.”

“We are one day away from changing the United States of America,” he added, hammering the economy anew as polls gave him a commanding lead across the political map.

McCain, meanwhile, was racing through seven states in a last campaign swing that ends today morning, in a bid to persuade undecided voters that he, not his rival, was more qualified to lead the US. “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.

Most national polls show Obama ahead of McCain, and state surveys suggest the Democrat’s path to the requisite 270 electoral votes is much easier than McCain’s.

Nationwide, an Associated Press-Yahoo News national survey of likely voters put Obama ahead, 51 to 43, with a margin of error of plus or minus 3 percentage points. The Gallup Poll tracking survey calculated Obama’s margin at 10 percentage points, 52-42.

According to the AP-Yahoo poll, one in seven voters — 14 percent of the total — said they were undecided or might yet change their minds. The rule of thumb among pollsters is that undecided voters generally split evenly between the leading candidates.

This means that Obama, safely ahead in nearly all of the Democratic states, has the chance to win by a decisive margin — and that everything must break right for McCain in order for him to win.

McCain’s hopes hinge on winning all, or nearly all, the states that carried President George W. Bush to victory in 2004: Ohio, Florida, Indiana, Missouri and Virginia.

But polls show Obama winning or tied in more than a dozen or so states won by Bush while McCain trails in every state that went to Democratic candidate John Kerry.

The only major “blue,” or Democratic, state being contested is Pennsylvania, which the Democrats carried in the last four presidential elections.

If state-by-state polling and electoral map projections are accurate, McCain will need to win Pennsylvania and Ohio.

Ohio has voted for the winner of every election since 1960, when Republican Richard Nixon won the state by a margin of more than 6 percent, but John F. Kennedy won the White House.

Pennsylvania has sided with the Democratic loser in the last two elections, choosing Sen. John Kerry over President Bush in 2004 and former Vice President Al Gore over Bush in 2000.

A Republican has not won in Pennsylvania since 1988, when Bush’s father, George H.W. Bush, edged former Massachusetts Gov. Michael Dukakis by 100,000 votes. The neighboring battleground states account for 41 of the 270 electoral votes needed to win the election and are home to voters whose economic concerns and religious values transcend party affiliation.

According to recent polls a day before the election, Obama leads McCain in six of eight key battleground states, including the big prizes of Florida and Ohio.

Obama holds a 7-point edge over McCain among likely US voters in a Reuters/C-SPAN/Zogby national tracking poll, up 1 percentage point from Sunday.

— With input from agencies