Washington - The United States' teetering economic future was expected to be front and centre in the final debate Wednesday evening between Democratic presidential nominee Barack Obama and rival Republican candidate John McCain, who have spent the week sharpening their financial spears.

The round-table encounter at Hofstra University on Long Island outside New York City is seen by some as a last-chance bid by the centre-right McCain, 72, to rescue a flagging campaign.

Obama, 47, who is seeking to become the country's first African- American president, pulled ahead by 14 percentage points among likely voters in a new poll released Tuesday by CBS News/New York Times, after a poll earlier this week gave him a 10-point lead.

But much can change in the final three weeks before the election on November 4, and the two men released refined versions of their economic strategy this week as the US government took yet another unprecedented step to stabilize markets by buying up bank shares worth 250 billion dollars.

There could also be fireworks over the McCain campaign's attempt to paint Obama as a terrorist sympathizer because he served on a charitable board in recent years with Bill Ayers, the one-time leader of the 1960s leftist militant group the Weather Underground.

Obama, who was a child of 8 or 9 at the time Ayers was active in the group, has dismissed the attacks as a sign of desperation by his rival and suggested that McCain would not have the courage to raise the issue to his face.

But McCain was spoiling to take up the challenge Wednesday night, telling the St Louis, Missouri, radio station KMOX Tuesday that his rival could be "ensured that it will come up this time."

With voters' concerns focusing more intensely on the economy and the dwindling prospects for their own jobs and retirement security amid the worst global economic crisis since the Great Depression of the 1930s, Obama has gained ground in polling, pulling from a near-draw with the Vietnam War hero in mid-September to his current lead.

Obama has pledged throughout his campaign to make middle-class tax cuts, invest in green technology to create jobs, implement tax advantages for job creation inside the United States, carry out a public works programme to restore crumbling infrastructure and help homeowners threatened by foreclosure.

On Tuesday, McCain grabbed headlines with his pledge of a 52.5-billion-dollar programme to cut taxes, reform rules to help investors saving for retirement and reduce the capital gains taxes.

But McCain did not bring up again his much-criticized proposal to buy up all bad US home mortgages, and his overall plan was seen by some as too little, too late.

US presidential elections are really 50 individual state contests for their winner-take-all electoral votes. In the indirect US election system for president, the states choose electors, who then choose the president on December 15.

In eight of 11 states swept by US President George W Bush in 2004, Obama has now edged ahead, including in the large states of Ohio, Virginia and Florida, according to polling averages calculated by the website organization realclearpolitics. com.

However, many of the polling results are within the margin of statistical error. (dpa)