John McCain, needing a dramatic turnaround to his waning White House hopes, vowed to unmask his rival Barack Obama as a radical sympathizer at their third and final debate in New York Wednesday.

Ahead of the evening debate at Hofstra University on Long Island, the New York Daily News tabloid ran a front-page caricature of a gun-toting McCain emerging from a Wild West bar, under the headline "Last Chance Saloon."

McCain, who was down a whopping 14 points in one new poll as the United States weathers its worst financial crisis in decades, talked tough heading into the last presidential debate before the November 4 vote.

At the weekend, McCain promised supporters he would "whip" his Democratic opponent's "you know what" during the debate starting at 0100 GMT.

On Tuesday, as he issued the latest version of his plan to end the financial tumult, the Arizona senator vowed to bring up Obama's links to 1960s radical turned Chicago education professor William Ayers.

"It's not that I give a damn about some old washed-up terrorist and his terrorist wife," McCain, 72, told KMOX radio in Saint Louis, Missouri.

"What I care about and what the American people care about is whether he (Obama) is being truthful with the American people."

Senior McCain adviser Nicolle Wallace told NBC television early Wednesday: "We've never been interested in negative attacks for the purpose of negative attacks. But the truth has to stand on its own tonight."

However, as millions of voters fret about possibly losing their jobs and health care, the perils of a negative strategy from McCain are clear as Obama, 47, builds up a commanding lead in several polls.

A New York Times-CBS News poll late Tuesday had the Illinois senator ahead of McCain by the huge margin of 14 points, 53 to 39 percent, compared to a lead of just three points before last week's second presidential debate.

At that debate, McCain jabbed his finger and spat out "that one" in Obama's direction. But the Democrat kept his cool, and snap polls gave him a second victory after his assured performance in the first debate in late September.

CBS said 21 percent of respondents now had a less favorable view of McCain in light of his Ayers-related character attacks on Obama and his choice of Alaska Governor Sarah Palin as running mate.

Nearly seven in 10 cited the economy as their top concern in a survey by the Los Angeles Times and Bloomberg that showed Obama was ahead by nine points, 50 to 41 percent.

"Even though Senator McCain has said he doesn't 'give a damn' about Bill Ayers, his campaign has admitted that if he talks about the economy, he'll lose," Obama spokesman Bill Burton said.

"On the big issues, this debate is one last chance for John McCain to do what he has failed to do throughout this entire campaign: explain to the American people how his economic policies would be any different at all than the failed Bush agenda he has supported every step of the way," he said.

Ayers and his wife Bernadine Dohrn were part of a group of anti-Vietnam War militants called the Weather Underground that bombed government buildings in the late 1960s and early 1970s.

McCain says the professor was instrumental in Obama's political rise from the mid-1990s, a claim dismissed by the Democrat's camp as wildly exaggerated. It says the pair were only loosely connected in Chicago charitable work.

Quinnipiac University polls Tuesday suggested Obama has broken through the 50-percent threshold in four of the most important battleground states: Colorado, Michigan, Minnesota and Wisconsin.

McCain's adviser Wallace acknowledged the polls looked bleak.

"And John McCain has been here before. The landscape was pretty similar, actually, far more bleak during the Republican primaries," the former White House communications chief said.

"So I think he's talked about how Americans need to take these final three weeks and really ask themselves do they want someone who has a record of fighting for them?" she said.

"Or do they want someone who says one thing and does another?"