He answered emerging questions about why the U.S. didn't send more firepower, such as gunships or fixed-wing fighter jets. He said those were not in the vicinity and would have required at least nine to 12 hours to deploy. Even if aircraft could have arrived quickly, the chaos would have prevented them from getting the accurate information they needed to hit the right targets, he said.
Sen. Kelly Ayotte, R-N.H., pressed Dempsey on why F-16 jets in Aviano, Italy, weren't sent to Libya. Dempsey said it would have taken up to 20 hours to get the planes ready and on their way, and he added that they would have been the "wrong tool for the job."
Dempsey reminded the committee that it was "9/11 everywhere" when the consulate was attacked and that U.S. armed forces were prepared to respond to a wide variety of threats around the world.
U.S. posts and facilities in many countries throughout Africa and southwest Asia were operating under heightened protection levels, he said. "We positioned our forces in a way that was informed by and consistent with available threat estimates," Dempsey said.
Sen. Saxby Chambliss, R-Ga., asked whether Panetta and Dempsey would describe the Benghazi incident as an "intelligence failure."
Panetta stopped short of using that term, saying simply that "some of the initial assessments were not on the money." Dempsey called it an "intelligence gap."
Sen. James Inhofe, the committee's top Republican, wasted little time in criticizing the administration for trying to "cover up" what he said was clearly a terrorist attack. The U.S. ambassador to the United Nations, Susan Rice, initially attributed the violence to a protest against an American-made, anti-Islam video.
Rice's comments touched off a deeply partisan feud, with Republicans claiming the Obama White House wanted to obscure the reasons for the incident to help the president's re-election bid. The criticism of Rice was largely responsible for scuttling her chances to become secretary of state.
"An angry mob doesn't use coordinated mortars and RPGs," Inhofe said, using the acronym for rocket-propelled grenades.
Panetta is retiring after a Washington career that has stretched across four decades, with years as a California congressman, budget chief, White House chief of staff to President Bill Clinton and CIA director who oversaw the hunt for and killing of terrorist leader Osama bin Laden.
The Defense Department will bid farewell to Panetta, who has served as defense secretary since June 2011, in a ceremony on Friday. The committee gave Panetta a round of applause as Chairman Carl Levin, D-Mich., praised the Pentagon chief's integrity. President Barack Obama has nominated former Republican Sen. Chuck Hagel to succeed Panetta.
Associated Press writer Lolita C. Baldor contributed to this report.