(AP) - John McCain assailed Barack Obama'scharacter and his campaign positions on taxes, abortion and moreWednesday night, hoping to turn their final presidential debateinto a launching pad for a political comeback. "You didn't tellthe American people the truth," he said.

Unruffled, and ahead in the polls, Obama parried each charge,and leveled a few of his own.

"One hundred percent, John, of your ads, 100 percent of themhave been negative," Obama shot back in an uncommonly personaldebate less than three weeks from Election Day.

"It's not true," McCain retorted.

"It is true," said Obama, seeking the last word.

McCain is currently running all negative ads, according to astudy by the University of Wisconsin-Madison. But he has run anumber of positive ads during the campaign.

The 90-minute encounter, at a round table at Hofstra University,was their third debate, and marked the beginning of a 20-day sprintto Election Day. Obama leads in the national polls and in surveysin many battleground states, an advantage built in the weeks sincethe nation stumbled into the greatest economic crisis since theGreat Depression.

With few exceptions, the campaign is being waged in states thatvoted Republican in 2004 - Virginia, Colorado, Iowa - and in manyof them, Obama holds a lead in the polls.

McCain played the aggressor from the opening moments of thedebate, accusing Obama of waging class warfare by seeking taxincreases that would "spread the wealth around."

The Arizona senator also demanded to know the full extent ofObama's relationship with William Ayers, a 1960s-era terrorist andthe Democrat's ties with ACORN, a liberal group accused ofviolating federal law as it seeks to register voters. And heinsisted Obama disavow last week's remarks by Rep. John Lewis, aDemocrat, who accused the Republican ticket of playing racialpolitics along the same lines as segregationists of the past.

Struggling to escape the political drag of an unpopularRepublican incumbent, McCain also said, "Sen. Obama, I am notPresident Bush. ... You wanted to run against President Bush, youshould have run four years ago."

Obama returned each volley, and brushed aside McCain's claim tofull political independence.

"If I've occasionally mistaken your policies for George Bush'spolicies, it's because on the core economic issues that matter tothe American people - on tax policy, on energy policy, on spendingpriorities - you have been a vigorous supporter of PresidentBush," he said.

McCain's allegation that Obama had not leveled with the publicinvolved the Illinois senator's decision to forgo public financingfor his campaign in favor of raising his own funds. As a result, hehas far outraised McCain, although the difference has been somewhatneutralized by an advantage the Republican National Committee holdsover the Democratic Party.

"He signed a piece of paper" earlier in the campaign pledgingto accept federal financing, McCain said. He added that Obama'scampaign has spent more money than any since Watergate, a referenceto President Nixon's re-election, a campaign that later becamesynonymous with scandal.

Obama made no immediate response to McCain's assertion abouthaving signed a pledge to accept federal campaign funds. Asked about running mates, both presidential candidates saidDemocrat Joseph Biden was qualified to become president, althoughMcCain added this qualifier: "in many respects."

McCain passed up a chance to say his own running mate, AlaskaGov. Sarah Palin, was qualified to sit in the Oval Office, thoughhe praised her performance as governor and noted her work on behalfof special needs children. The Palins have a son born earlier thisyear with Down Syndrome.

Obama sidestepped when asked about Palin's qualifications toserve as president, and he, too, praised her advocacy for specialneeds children.

But he quickly sought to turn the issue to his advantage bynoting McCain favors a spending freeze on government programs. "I do want to just point out that autism, for example, or otherspecial needs will require some additional funding if we're goingto get serious in terms of research. ... And if we have anacross-the-board spending freeze, we're not going to be able to doit," he said.

The entire debate can be seen on-demand in the iO Extra category of News 12 Interactive, Channel 612 on your iO digital cable box.