WASHINGTON (AP) — Defense Secretary Leon Panetta said Thursday that the speed of the attack on the U.S. diplomatic mission in Benghazi, Libya, kept U.S. armed forces from responding in time to save the four Americans who were killed as the Pentagon chief defended the military's response on a chaotic Sept. 11 day.

Testifying for likely the last time on Capitol Hill before stepping down, Panetta said the Obama administration was trying to assess the threat from protests in Tunisia, Egypt, the Libyan capital of Tripoli and other countries while trying to move quickly to respond to two separate assaults six hours apart in Benghazi.

The positioning of military teams far from the U.S. installation made it difficult to respond swiftly, he said. The assault claimed the lives of Ambassador Chris Stevens and three other Americans.

"The United States military is not and should not be a global 911 service capable of arriving on the scene within minutes to every possible contingency around the world," Panetta told the Senate Armed Services Committee.

Army Gen. Martin Dempsey echoed the argument that the military did what its location allowed, which angered Sen. John McCain, R-Ariz., who accused the Joint Chiefs of Staff chairman of peddling falsehoods.

"For you to testify that our posture did not allow a rapid response, did not take into account threats to our consulate ... is simply false," McCain told Dempsey. McCain contended that the military's capability allowed armed forces to intervene in short order.

Dempsey said he stood by his testimony, "your dispute of it notwithstanding." The general said the military was concerned with multiple threats worldwide and, based on time and positioning of forces, "we wouldn't have gotten there in time."

Between midnight and 2 a.m. on the night of the attack, Panetta issued orders, telling two Marine anti-terrorism teams based in Rota, Spain, to prepare to deploy to Libya, and he ordered a team of special operations forces in Central Europe and another team of special operations forces in the U.S. to prepare to deploy to a staging base in Europe.

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The first of those U.S. military units did not actually arrive in the region until well after the attack was over and Americans had been flown out of the country. Just before 8 p.m., the special operations team landed at Sigonella Naval Air Station in Sicily. An hour later, the Marine team landed in Tripoli. Defense officials have repeatedly said that even if the military had been able to get units there a bit faster, there was no way they could have gotten there in time to make any difference in the deaths of the four Americans.

"This was, pure and simple, a problem of distance and time," Panetta said.

Committee Republicans used the hearing to highlight their months of repeated criticism of President Barack Obama and the administration, claiming officials ignored warnings and even suggesting that the commander in chief was disengaged from what was happening during the hours of the two attacks.

Panetta said he and Dempsey were meeting with Obama when they learned for the Libya assault. He said the president told them to deploy forces as quickly as possible.

In one testy exchange, Sen. Lindsey Graham, R-S.C., questioned whether Panetta spoke again to Obama after that first meeting. The Pentagon chief said no but that the White House was in touch with military officials and aware of what was happening.

"During the eight-hour period, did he show any curiosity?" Graham asked.

Panetta said there was no question the president was concerned about American lives. Exasperated with Graham's interruptions, Panetta said forcefully, "The president is well-informed about what is going on; make no mistake about it."

Panetta also pushed back against Republican criticism that the Obama administration ignored warning signs about the attack. The Pentagon chief insisted there were no signs of or specific intelligence about an imminent attack. Six months prior to the assault, the government was apprised of 281 threats to diplomatic missions, consulates and other facilities worldwide, he said.

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.

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Associated Press writer Lolita C. Baldor contributed to this report.