Panetta also predicted that his designated successor, former Republican Sen. Chuck Hagel of Nebraska, will be confirmed by the Senate, despite questions raised by many about his views on Israel and Iran.
"I think a lot of the criticisms that are being made right now are unfair," Panetta said, adding that he would leave it to Hagel to address these at his Senate confirmation hearing, the date for which has not yet been set.
"In these confirmation battles there are a lot of charges that will be out there," he added. "There will be a lot of criticisms that are out there. But ultimately, the truth prevails. And I think the truth in this case will mean that he'll be confirmed."
Panetta said he is confident, after having met with Hagel to discuss their transition, that the Vietnam War veteran is committed to the plan for gradually shifting responsibility for Afghanistan's security to Afghan forces so that foreign forces can leave in two years.
Panetta told a news conference that he and Karzai had lain the groundwork for the Afghan leader's meeting at the White House on Friday with President Obama. That session is not expected to clarify the size of any U.S. military role in Afghanistan after 2014, but it may spell out examples of U.S. aid.
"We made very good progress on, you know, the kind of equipment that we would try to make available to them," to enable the Afghans to not only secure their borders but also prevent a Taliban takeover, Panetta said.
Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told the same news conference that U.S. and Afghan officials are developing a common assessment of threats Afghanistan is likely to face. Conclusions from that study will help determine Afghanistan's military requirements, he said.
U.S. commanders in Afghanistan have proposed options for keeping between 6,000 and 15,000 U.S. troops in Afghanistan after 2014 to continue pressuring terrorists and develop Afghan security forces. But the White House has aimed even lower, telling reporters on Tuesday that Obama would be open to the possibility of withdrawing entirely in 2014, so long as he can be confident that Afghanistan can stand on its own.