WASHINGTON (CNN) -
At a congressional hearing Wednesday loaded with political implications, a top State Department official will defend the administration's handling of the terrorist attack in Libya that killed U.S. Ambassador Christopher Stevens and three other Americans on the anniversary of 9/11.
Prepared testimony made public before the House Oversight Committee hearing showed that Under Secretary of State for Management Patrick Kennedy will address specific criticism by Republicans of an alleged lack of preparedness ahead of the Benghazi consulate attack and a shifting response by the Obama administration following the assault.
"The Department of State regularly assesses risk and allocation of resources for security; a process which involves the considered judgments of experienced professionals on the ground and in Washington, using the best information available," Kennedy's prepared statement said. "The assault that occurred on the evening of September 11, however, was an unprecedented attack by dozens of heavily armed men."
He also will tell the Republican-led panel that initial assessments by administration officials about what happened that night were based on available information that has since changed.
Critics accuse the administration of trying to cover up or play down the attack through initial statements that described it as a spontaneous act stemming from protests over an anti-Muslim film rather than a planned terrorist assault.
"We have always made clear that we are giving the best information we have at the time. And that information has evolved," Kennedy's prepared statement said, citing remarks by U.N. Ambassador Susan Rice on September 16 that critics alleged were deceptive. "The information she had at that point from the intelligence community is the same that I had at that point. As time went on, additional information became available."
GOP challenger Mitt Romney has made the Libya attack a focus of his criticism of President Barack Obama's foreign policy.
With polls showing more people favor Obama over Romney on foreign policy, the former Massachusetts governor seeks to gain ground by arguing the president has made America less influential and more vulnerable around the world.
The assault in Benghazi occurred 11 years to the day after the September 11, 2001, attacks on New York's World Trade Center and the Pentagon. After initially blaming the violence on the protest over the film produced in America, the Obama administration conceded it was a terrorist attack.
In Kennedy's prepared statement, he noted that Secretary of State Hillary Clinton appointed an Accountability Review Board that includes well-known figures such as former Joint Chiefs Chairman Adm. Michael Mullen to report on whether proper security systems and procedures were in place or implemented
"Until these investigations conclude, we are dealing with an incomplete picture, and, as a result, our answers today will also be incomplete," Kennedy's prepared statement said.
The House panel scheduled the hearing even though Congress is on recess until after next month's election. Also set to testify were Deputy Assistant Secretary of State for International Programs Charlene Lamb; Regional Security Officer Eric Nordstrom, who was stationed in Libya before the attacks; and Lt. Col. Andrew Wood, a Utah National Guardsman who was leading a security team in Libya until August.
Issa's committee had asked Clinton to take part, and she sent Kennedy and Lamb to appear.
Democrats accuse Issa of planning a partisan hearing, a similar allegation leveled against the panel for its past investigations of the botched "Fast and Furious" gun-running program and the failed Solyndra clean energy company that received about $500 million in government loan guarantees.
On Tuesday, two senior State Department officials provided reporters with the most detailed explanation yet of the attack in Benghazi, telling a conference call that there was no prior indication such an assault was imminent.
The officials, who briefed reporters on condition of not being identified by name, said there was "nothing unusual" throughout the day of the attack.
Stevens held an evening meeting with a Turkish diplomat and then retired to his room in one of the compound's buildings at 9 p.m., according to the officials. The first sign of a problem came 40 minutes later when diplomatic security agents heard loud talking outside the compound, along with gunfire and explosions.
Asked whether the attack was a spontaneous assault taking advantage of a demonstration, as originally asserted by Obama administration officials, one senior official said, "That was not our conclusion."
The two senior officials offered riveting detail of the attack by what one of them described as "dozens of armed men" who marauded from building to building in the enormous complex and later fired mortars on a U.S. annex less than a mile away.
the havoc at the compound, which had four buildings, Stevens and two of his security personnel took refuge in a fortified room that the attackers were able to penetrate, one official said.
The attackers doused the building with diesel fuel and set it ablaze, and the three men decided to leave the safe haven and move to a bathroom to be able to breathe, according to the official. Stevens became separated from the security personnel in the chaos and smoke, and eventually turned up at a Benghazi hospital, where he was declared dead.
Hospital personnel found his cell phone in his pocket and began calling numbers, which is how U.S. officials learned where he was, the State Department officials said.
The officials echoed what administration officials have maintained since the attack: that U.S. and Libyan security personnel in Benghazi were outmanned and that no reasonable security presence could have fended off the assault.
"The lethality and the number of armed people is unprecedented," one official said. "There had been no attacks like that anywhere in Libya -- Tripoli, Benghazi or anywhere -- in the time that we had been there. And so it is unprecedented, in fact, it would be very, very hard to find precedent for an attack like (it) in recent diplomatic history."
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