* Obama's weak debate raises the stakes for Biden-Ryan clash
* Democrats hope Biden can blunt Republican momentum
* Biden more experienced, but has history of gaffes
(Updates with new polls, edits)
By John Whitesides
DANVILLE, Ky., Oct 11 (Reuters) - Democrats are betting onU.S. Vice President Joe Biden to deliver a feisty performanceThursday evening during a high-stakes debate against Republicanchallenger Paul Ryan and seize back momentum in the race for theWhite House.
Republican Mitt Romney's steady climb in polls sincePresident Barack Obama's poor showing in their first debate lastweek have intensified expectations for the vice presidentialshowdown with less than four weeks before the Nov. 6 election.
The former Massachusetts governor has taken the lead innational surveys and narrowed the gap by which he trails Obamain many of the swing states that will decide the election.
Romney led the Democratic incumbent by 47 percent to 44percent in the Reuters/Ipsos daily tracking poll on Thursday -the online poll showed the challenger with a one percentagepoint advantage on Wednesday.
Several new swing-state polls released on Thursday alsoshowed Romney edging closer to Obama among likely voters. Obamahad a six-point lead in an Ohio poll and a five-point lead in aVirginia survey. Separate polls in Virginia, Colorado, Floridaand Wisconsin had gaps of three points or less.
Biden, 69, a veteran politician and accomplished debaterknown for delivering withering attacks with a smile, will try toimprove the outlook for the Democrats before Romney and Obamameet for a second televised debate next Tuesday.
The 42-year-old Ryan, who has served seven terms in the U.S.House of Representatives and is chairman of the House BudgetCommittee, has been criticized for being a cautious campaignersince Romney chose him as his running mate in August. TheWisconsin congressman will look to ward off Biden's attackswhile avoiding his own tendency to get mired in numbers.
Foreign policy is expected to be a ripe topic. Republicansare eager to take the Obama administration to task over lastmonth's attacks on U.S. diplomatic missions in the Middle East,and Biden will be ready to point out the lack of foreign policyexperience on the Romney-Ryan ticket.ï¿½ Biden is expected to challenge Ryan on his and Romney'sassertions on taxes, health care and other key issues, somethingthat Democrats felt Obama largely let slide during the debatelast week.
"This has turned into a legitimate high-stakes debatebecause the ground has shifted so profoundly on the Democrats,"said Cal Jillson, a political scientist at Southern MethodistUniversity in Texas.
"Biden at least has to hold his own so panic doesn't set infor Democrats," he said. "They don't want to lose two in a row."
Biden and Ryan meet at 9 p.m. EDT (0100 GMT on Friday) inthe nationally televised debate from Centre College in Danville,Kentucky.
Romney has shifted more toward the political center onabortion, taxes and other hot-button issues, starting with lastweek's debate, and thousands of people have turned out for himat campaign appearances since.
Democrats have accused the Republican, who called himself a"severe conservative" while vying for his party's presidentialnomination, of shifting or misrepresenting his positions. Bidenis expected to be more confrontational than Obama in anencounter that covers both domestic and foreign policy.
"It's a great opportunity, again, to drive the distinctionsbetween the two candidates and talk about distinct approaches tothe future," Obama campaign deputy manager Stephanie Cutter saidon MSNBC's "Morning Joe" program.
"Right now the Romney campaign is running away from some oftheir positions like unwanted stepchildren, but we're going tohold them to them and explain to the country exactly what thedifferences are here because the choice is very stark," shesaid.
As he boarded Air Force Two on Thursday morning to fly toKentucky for the debate, Biden told reporters he was ready forthe face-off. "I'm looking forward to it," he said.
'JOE JUST NEEDS TO BE JOE'
Biden, the former chairman of the Senate Foreign Relationsand Judiciary committees, has more experience on the nationalstage than Ryan.
He was a strong performer in the Democratic primary debatesduring his failed 2008 run for the White House and fared wellagainst Republican Sarah Palin in that year's vice presidentialdebate.
But he also has a reputation for gaffes, including a recentremark that the middle class has been "buried for the last fouryears" - almost the span of Obama's presidency - by a badeconomy.
Obama said he was not worried about Biden.
"I think Joe just needs to be Joe. Congressman Ryan is asmart and effective speaker. But his ideas are the wrong onesand Joe understands that," Obama said in an interview with ABCNews on Wednesday.
Ryan's previous debate experience consists of congressionalcontests in Wisconsin. He was happy to raise expectations forBiden's performance.
"Sure it's a nervous situation. Joe Biden's one of the mostexperienced debaters we have in modern politics," Ryan toldreporters. "But the Achilles' heel he has is President Obama'srecord."
Ryan's budget plan, which has made him a hit withconservatives, is likely to play a starring role in the debate.Ryan proposes slashing government spending and creating a"voucher" system for the Medicare healthcare program forseniors, which Democrats say would leave some retirees payingmore of their medical costs.
"The challenge for Biden, and Obama didn't do this at all,is to put the other side on the defensive and make them explainthemselves and their policies," said Steven Schier, a politicalscientist at Carleton College in Minnesota.
Biden said he has been studying Ryan's plan during hisdebate preparations. Democratic U.S. Representative Chris VanHollen has played Ryan in mock debates, while Ryan has beenprepared by former U.S. Solicitor General Ted Olson.
(Additional reporting by Susan Heavey in Washington and JeffMason in Delaware; Writing by John Whitesides and PatriciaZengerle; Editing by Alistair Bell, Karey Wutkowski and PaulSimao)
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