* Biden aggressively defends administration's record
* Ryan accuses Obama of weakness in leadership
* Democrats hope Biden can blunt Republican momentum
(Adds details, quotes) By John Whitesides and Andy Sullivan
DANVILLE, Ky., Oct 11 (Reuters) - Vice President Joe Bidenand rival Republican Paul Ryan clashed sharply over foreignpolicy in a high-stakes debate on Thursday, with Bidenaggressively defending the Obama administration's policies anddismissing Ryan's criticism as "malarkey."
Biden took the offensive early, providing the emotion andpassion that President Barack Obama was criticized for lackingin last week's debate with Republican challenger Mitt Romney.
Ryan accused the Obama administration of projecting an imageof American weakness to the world.
"With all due respect, that is a bunch of malarkey," Bidenretorted, attacking Romney as "not presidential" for holding anews conference on Libya just after a U.S. diplomatic compoundwas attacked and the ambassador killed.
Democrats were counting on an aggressive performance fromBiden to reclaim the momentum in the race for the White Houseafter Obama's poor showing led to Romney taking the lead inpolls with less than four weeks before the Nov. 6 election.
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 both candidatesaggressively went after each other.
SMIRKING, INTERRUPTIONS The atmosphere was tense.
Biden interrupted his opponent frequently and laughed atmany of Ryan's answers, while the Republican smirked as Bidenspoke.
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.
He said the gaffe-prone Biden should understand that"sometimes the words don't always come out the right way."
Biden smiled but shot back: "I always say what I mean."
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.
Biden was a strong performer in the Democratic primarydebates during his failed 2008 run for the White House and faredwell against Republican Sarah Palin in that year's vicepresidential debate.
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/