WASHINGTON - AMERICANS vote in an election of rare historic potential on Tuesday with front-running Democrat Barack Obama seeking to become the first black president and Republican John McCain hoping for a poll-defying comeback.

After an epic campaign, voters could also spark a political realignment in Washington, with Democrats targeting big gains in the Senate and House of Representatives, after eight turbulent years under President George W. Bush.

History's longest, most costly White House campaign ends with Democrat Obama the hot favorite, with wide leads in national polls and the edge in a string of battleground states which could swing the election either way.

In the eye of the worst financial storm since the 1930s and with US troops embroiled in wars in Iraq and Afghanistan, both Mr Obama and Mr McCain have vowed to restore the frayed self-confidence of the world's lone superpower.

Both Mr Obama and Mr McCain will be chasing the 270 electoral votes needed across the diverse state-by-state electoral map to take the White House with more than 100 million people trekking to the polls to add to 30 million advance votes already cast.

The tiny New Hampshire town of Dixville Notch played its traditional role of hosting the first election day voting just after midnight (0500 GMT, 1pm Singapore time), according to national television.

Another town in the state, Hart's Location, was to do likewise, according to electoral tradition.

Hours later, the rest of the United States will follow suit, with first results not expected until 7.00pm eastern time (2300 GMT, 7pm Singapore time).

Mr Obama and Mr McCain, one of whom will become the first sitting senator elected president since John F. Kennedy in 1960, careened to the finish line on Monday, with competing cross-country campaign blitzes.

'We are one day away from changing the United States of America,' Mr Obama, 47, said in Florida, before heading off to whip up crowds in North Carolina and Virginia, hoping to squeeze his rival on normally Republican territory.

But Mr McCain was defiant, vowing to confound pollsters and pundits and overcome a treacherous political map which has him struggling to cling onto Republican bastions and on which one big loss could make Mr Obama president.

'The Mac is back!' he roared at his campaign stops, promising a stunning act of political escapology that would confound almost every major opinion poll.

The Republican nominee raced through Florida, Virginia, Pennsylvania, Tennessee, Indiana, New Mexico and Nevada before heading home to Arizona for election day.

But the fact that all but Pennsylvania of those states was carried by Mr Bush in 2004 reflects the fact that Mr Obama was the candidate with the momentum heading into election day.

Senator Obama, the son of a Kenyan father and white mother from Kansas, would become the first African American president, after an stunning rise to the pinnacle of US politics - he was not even a Senator four years ago.

In a tragic turn of events Monday, Mr Obama learned that Madelyn Dunham, the white grandmother who had brought him up, had died in his native Hawaii from cancer, aged 86.

Mr Obama built a huge grass roots political movement which he hopes will drive millions of first time voters to the polls and stifle Mr McCain's comeback hopes.

He promises to alleviate the economic pinch for the middle class with 'a new politics for a new time' and repair ties with US allies, open talks with foes like Iran and Cuba, bring troops home from Iraq and refocus on the Afghan war.

Mr McCain, leveraging his heroism as a Vietnam war prisoner and decades of experience in Washington, would be the oldest president, at 72, inaugurated for a first term.

He has lambasted Mr Obama for 'socialist' tax policies, and argues his rival is unprepared for an age of global turmoil and would pursue a more hawkish line towards US enemies and Russia.

Mr McCain though has lambasted Bush policies on climate change and savaged the early conduct of the Iraq war.

He parried Mr Obama's crusade for change by running as a maverick - but the Democrat seems to have saddled him with Mr Bush's unpopular legacy.

Mr McCain's pick of untested Alaska Governor Sarah Palin as his running mate was also controversial and prompted Mr Obama to label him as erratic.

With polls showing 90 per cent of voters believe America is on the wrong track, Mr Obama should be a lock for victory - but whether his race or lack of experience could give voters pause is an intangible.

Polls make Mr Obama the hot favourite, though McCain aides dispute the numbers and point to a late tightening of surveys in key states to argue he can still win.

A new Wall Street Journal-NBC News poll put Mr Obama ahead 51 per cent to 43. A Washington Post-ABC News poll said the race was so far Obama's by 54 per cent to 43, and Rasmussen said had him up 51 per cent to Mr McCain's 46.

The final Gallup Daily tracking poll before the election day said Mr Obama was leading the race 53 per cent to 42 per cent.

The Democrat has an easier path to the 270 electoral votes and has a small but solid lead in many of the battleground states needed to win the White House and may be building an advantage as millions of Americans vote early. -- AFP

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