* Biden aggressively defends administration's record
* Ryan accuses Obama of weakness in leadership
* Democrats hope Biden can blunt Republican momentum
(Adds details and quotes throughout)
By John Whitesides and Andy Sullivan
DANVILLE, Ky., Oct 11 (Reuters) - U.S. Vice President JoeBiden and rival Republican Paul Ryan battled fiercely overforeign policy and the economy in a lively debate on Thursday,with Biden aggressively defending the administration's policiesand dismissing Ryan's criticism.
Seeking to win back the momentum for the Democrats' campaignafter a poor debate performance by President Barack Obama lastweek, Biden frequently went on the attack.
"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.
But Wisconsin congressman Ryan, almost 30 years younger thanhis vastly experienced opponent, held his own in a series oftesty exchanges.
The Republican joked that the gaffe-prone Biden shouldunderstand that "sometimes the words don't always come out theright way."
Biden took the offensive early, providing the emotion andpassion that Obama was criticized for lacking in last week'sdebate with Republican challenger Mitt Romney.
Ryan stood his ground, and the vice presidential candidatesfor the Nov. 6 election frequently interrupted each other andtalked at the same time.
In body language that might not go down well with undecidedvoters, Biden smiled and laughed sarcastically at points duringthe 90-minute debate in an apparent effort to dismiss Ryancomments.
Ryan said Americans were seeing the "unraveling" of Obama'sforeign policy, and Biden attacked Romney as "not presidential"for holding a news conference on Libya just after a U.S.diplomatic compound was attacked and the ambassador killed.
Democrats were counting on a forceful performance from Bidento reclaim the momentum in the race for the White House afterObama's poor showing led to Romney taking the lead in polls withless than four weeks before the Nov. 6 election.
"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."
Ryan said the Obama administration had given confusinginformation about the killing last month of the U.S. ambassadorto Libya, Christopher Stevens.
"It took the president two weeks to acknowledge that thiswas a terrorist attack," the Wisconsin congressman said.
Biden vowed the administration would find the perpetratorsof the attack and rectify mistakes in security at the diplomaticmission in Benghazi.
The two candidates sat across from each other at a table butthe proximity did not lessen the conflict, as they aggressivelywent after each other.
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 42-year-old Ryan, a seven-term congressman and chairmanof the House of Representatives Budget Committee, is popularwith conservatives for a budget plan that would slash governmentspending and creating a "voucher" system for the popularMedicare healthcare program for seniors. Democrats say it wouldleave some retirees paying more of their medical costs.
"We will not be part of any voucher plan, or theprivatization of Social Security," Biden said.
Biden, 69, the former chairman of the Senate ForeignRelations and Judiciary committees, clearly was ready to pointout the lack of international experience on the Romney-Ryanticket.
Obama set an aggressive tone before the Biden-Ryan debate,accusing Romney of shifting toward the political center despitetouting conservative credentials during the long Republicannomination contest.
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.
(Editing by Alistair Bell and Christopher Wilson)
Keywords: USA CAMPAIGN/