Panetta said that U.S. officials learned in the months after the incident that "there were actually two short-duration attacks that occurred some six hours apart," the first on the consulate and the second on an annex two miles away.

"The bottom line is this: That we were not dealing with a prolonged or continuous assault, which could have been brought to an end by a U.S. military response, very simply, although we had forces deployed to the region," he said.

Dempsey said he could not have gotten troops on the ground within 13 to 15 hours.

Panetta was firm throughout his testimony that there were no "undue delays" in decision making and there was no denial of support from Washington or from the military combatant commanders when the attack happened.

"Quite the contrary: The safe evacuation of all U.S. government personnel from Benghazi 12 hours after the initial attack" and transfer to the Ramstein Air Base in Germany "was the result of exceptional U.S. government coordination."

He said the U.S. military response helped save lives.

Obama's talk with Panetta

In the months since the attacks, Washington has been a center of debate about how much the State Department had known about threats in the region and whether, after the attacks, the administration tried to mislead the public about its nature.

An independent review released in December lambasted the State Department, saying "systemic failures and leadership and management deficiencies" led to inadequate security at the Benghazi post.

In his remarks, Panetta said the initial reports of the attack were given "almost immediately" to the U.S. Embassy in the Libyan capital of Tripoli.

Within 17 minutes, Panetta said, an unarmed, unmanned surveillance aircraft was dispatched to give U.S. officials a better idea of what was happening. It arrived at the site about 70 minutes after the attack, he said.

Soon, Panetta and Dempsey met with President Barack Obama, the secretary told lawmakers.

Obama ordered that the Defense Department respond to the attack with "all available DOD assets" and try to protect U.S. personnel, Panetta said.

Ayotte and Sen. Lindsey Graham, R-South Carolina asked how many times Obama spoke with Panetta and Dempsey after learning about the attack.

Once, in a half-hour conversation with the president, the men said; Obama did not personally get back in touch with them to ask how the mission to help personnel in Benghazi was going.

"Do you think it's a typical response of the president of the United States to make one phone call, do what you can and never call you back again and ask you, 'How is it going, by the way?'" Graham asked.

Panetta replied, "The president is well-informed about what is going on, make no mistake about it."

"Was any airplane launched in the world before the attack was concluded?" Graham asked.

"If you're talking about a strike aircraft, no, senator," Dempsey said.

"Did anybody leave any base anywhere to go to the aid of the people under attack in Benghazi, Libya, before the attack ended?" Graham asked.