WAUKESHA - With the final presidential debate taking place tonight and new poll numbers showing Democratic candidate Sen. Barack Obama taking a larger lead in more states, Republican candidate Sen. John McCain needs to make a very convincing argument in the final meeting between the two men.

Political experts say if McCain is unable to adequately present his plan on economic reform during tonight’s debate, Obama will have all but wrapped up the election in Wisconsin and possibly the country.

"It’s not entirely over yet. I think there’s still room for an evaluation of both Obama’s and McCain’s economic packages," said Joseph Foy, assistant professor of political science at the University of Wisconsin-Waukesha. "The debate is still important. The major swing for Obama in Wisconsin came after the last debate, and this one is still relevant and could have a big impact on the race."

The debate will take place at 8 p.m. today at Hofstra University in Hempstead, N.Y. It’s the third and final debate of the election between Obama and McCain.

Although McCain supporters have urged the campaign to begin hitting Obama for past associations, Foy said McCain doesn’t seem comfortable going into personal attacks. And even if he did, it wouldn’t help his campaign because only his base cares about those issues, Foy said.

The pressure has continued to mount on McCain, Foy said, because voters in the Great Lakes region are connecting more with Obama on economic issues, which are by far the most important issues for voters now.

Wednesday’s match-up has taken on a mano-a-mano flavor with McCain promising supporters that he will whip Obama’s ‘‘you-know-what’’ and Obama challenging McCain last week to ‘‘say it to my face.’’ He was referring to the McCain campaign’s assertions of late that Obama’s association with 1960s radical William Ayers calls the Illinois senator’s character into question.

In a radio interview Tuesday in Missouri, McCain said that Obama’s remark ‘‘probably ensures’’ that Ayers will come up in the debate. ‘‘It’s not that I give a damn about some old washed-up terrorist and his wife ... What I care about and what the American people care about is whether he (Obama) is being truthful with the American people,’’ McCain said.

With the economic crisis foremost in people’s minds, polls suggest that McCain has profited little from focusing on Obama’s Chicago associates. McCain may not need to bring up Ayers if moderator Bob Schieffer, of CBS, asks questions about character in following through with a vow to bring candidates out of the comfort zones of talking points.

But McCain has a fine line to walk, said Mitchell McKinney, a debate expert and communications professor at the University of Missouri. With ground to make up, McCain needs to be persuasive. But McKinney believes that it will take more than anger for McCain to win over the diminishing number of swing voters.

‘‘In some ways, he has to come out and be that happy warrior, a fighter,’’ McKinney said. ‘‘But projecting a mean or nasty image could feed a perception that he’s bitter and that this race is all over,’’ McKinney said.

On Tuesday, the latest Quinnipiac University poll came out, giving Obama a 17-point lead over McCain in Wisconsin. It’s Obama’s largest lead here and comes after the two men were in a statistical dead heat as little as a month ago.

A Republican candidate hasn’t carried the state since former President Ronald Reagan in 1984.

The poll also shows large leads for Obama in Minnesota, Colorado and Michigan with the election just three weeks away. One poll was done before last week’s debate and another was done after.

Post-debate polls showed Obama was up nine points in Colorado, 16 points in Michigan and 11 points in Minnesota.

‘‘Those margins may be insurmountable barring a reversal that has never been seen before in the modern era in which polling monitors public opinion throughout the campaign,’’ said Peter Brown, assistant director of the university’s polling institute. ‘‘Any realistic chance of McCain coming from behind depends on scoring a knockout in this week’s last debate. But given that he has been judged by the electorate to have lost both of the previous face-offs, that would seem to be a very tall order.’’

In the 2000 and 2004 elections, Democratic candidates carried Wisconsin by very narrow margins of 13,293 and 5,000 votes, respectively, over President George W. Bush.

However, Bush fared extremely well in Waukesha, beating Sen. John Kerry and former Vice President Al Gore by a two-to-one margin each election.

"(Obama’s lead) is surprising if you look at the last two elections and how close they were, but the economic realities have shifted since then" Foy said. "This is not the same political climate."

(McClatchy Newspapers contributed to this report.)