* Biden aggressively defends Obama administration's record
* Ryan accuses president of weakness in leadership
* Opinion divided on winner of debate
(Adds quotes, details) By John Whitesides and Andy Sullivan
DANVILLE, Ky., Oct 11 (Reuters) - U.S. Vice President JoeBiden leaped to the attack against Republican challenger PaulRyan in a lively debate on Thursday, aggressively defending theObama administration's economic and foreign policies to try toregain momentum in the White House race.
Biden was looking for a Democratic rebound after PresidentBarack Obama's poor debate performance last week. But theyounger and less experienced Ryan held his own in a series oftesty exchanges.
"With all due respect, that is a bunch of malarkey," Bidensaid when Ryan accused the White House of projecting an image ofAmerican weakness to the world.
First estimates of who prevailed at the debate in Kentuckywere split. A CBS News survey of undecided voters showed Bidenas the winner by 50 percent to 31 percent, while a CNN poll ofdebate watchers scored Ryan the victor by 48 percent to 44percent.
The vice presidential candidates in the Nov. 6 electionfrequently interrupted each other, talking at the same time andsometimes staring at each other in disbelief.
Biden grinned and laughed sarcastically at times, dismissingthe Wisconsin congressman's answers. But he repeatedly providedthe passion that Obama was criticized for lacking in last week'sdebate with Republican challenger Mitt Romney.
The White House race shifted in Romney's favor after thatencounter in Denver and he has taken the lead in some nationalpolls with less than four weeks before the election. AReuters-Ipsos online tracking poll on Thursday before the debateshowed Romney leading Obama by 47 percent to 44 percent.
"Mr. Vice President, I know you're under a lot of duress tomake up for lost ground, but I think people would be betterserved if we don't keep interrupting each other," Ryan said atone point.
"Well, don't take all the four minutes then," Bidenresponded. He later added: "I don't know what world this guy'sliving in."
'COULD NOT BE PROUDER'
Obama, who watched the debate on Air Force One whilereturning from a campaign trip, jogged out to meet reportersafter landing and praised his No. 2.
"I thought Joe Biden did terrific tonight. I could not beprouder of him. He made a very strong case," Obama said.
Romney called Ryan to congratulate him after the debate.
The fiery debate was likely to energize the base supportersof both parties, although Biden's smirks and dismissive commentswere risky.
"There's a fine line between showing passionate disagreementand showing obnoxiousness," said political scientist JamieChandler of Hunter College in New York.
Biden portrayed Ryan, the 42-year-old chairman of the HouseBudget Committee, as out of step with working Americans forsupporting a budget plan that slashes government spending andcreates a "voucher" system for the popular Medicare healthcareprogram for seniors.
"It will not keep pace with healthcare costs. Because if itdid keep pace with healthcare costs, there would be no savings,"Biden said. "We will be no part of a voucher program or theprivatization of Social Security."
Ryan said Democrats had not put a credible solution on thetable to address the long-range fiscal problems for Medicare."He'll say all these things to try and scare people," he said.
At one point, Ryan made reference to how President John F.Kennedy, a Democrat, had lowered tax rates. "Oh, now you're JackKennedy?" Biden asked.
Ryan pointed out that he and Biden were from similar towns -he is from Janesville, Wisconsin, and Biden from Scranton,Pennsylvania - and said unemployment had gone up in Scrantonsince Obama took office.
"That's how it's going all around America," Ryan said. Bidensaid Ryan had not read the recent statistics showingunemployment dropping to 7.8 percent nationally in September.
"That's not how it's going. It's going down," he said.
On foreign policy, Ryan said Americans were seeing the"unraveling" of Obama's approach, while Biden attacked Romneyfor holding a news conference on Libya last month just after theU.S. diplomatic compound was attacked and the ambassador killed.
Ryan said the Obama administration had given confusinginformation about the attack on the consulate in Benghazi, whichkilled U.S. Ambassador Christopher Stevens.
"It took the president two weeks to acknowledge that thiswas a terrorist attack," the Wisconsin congressman said.
Biden, 69, the former chairman of the Senate ForeignRelations Committees, pointed out the lack of internationalexperience on the Romney-Ryan ticket.
He vowed that the Obama administration would find theperpetrators of the attack and rectify mistakes in security atthe diplomatic mission.
The two candidates sat across from each other at a table butthe proximity did not lessen the conflict.
Ryan defended Romney's secretly recorded video condemningthe "47 percent" of the electorate that he said was dependent ongovernment and considered themselves victims, calling it amistake.
The Republican joked that the gaffe-prone Biden shouldunderstand that "sometimes the words don't always come out theright way."
(Editing by Alistair Bell and Christopher Wilson)
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