U.S. officials have said anywhere between zero to 9,000 U.S. forces could remain in Afghanistan past 2014.

During a hearing on Hagel's nomination in January, he spoke about Afghanistan.

"As to what kind of a force structure should eventually be in place by the Afghans, I don't know enough about the specifics to give you a good answer other than to say that I think that has to be a decision that is made certainly with the president of Afghanistan," he said.

Talking with Karzai will inform "what we can do to continue to support and train and protect our interests within the scope of our ability to do that," he said. "Obviously the immunity for our troops is an issue, which was an issue with Iraq. All those considerations will be important and will be made."

Hagel also said during that hearing that going to war in Iraq took the U.S. focus off Afghanistan.

The defense secretary knows from personal experience that good strategy must consider the human toll of war.

Before he became a two-term senator from Nebraska, a Georgetown professor or the head of a D.C. think tank, Hagel volunteered to join the Army and go to Vietnam.

As a sergeant, he was twice wounded and fought alongside his younger brother Tom.

Chuck Hagel earned two Purple Hearts. His brother patched up his wounds when he took shrapnel in the chest while on patrol, and Chuck Hagel saved his brother's life after Tom Hagel was wounded.

"I will do all I can to prevent war," he later told his biographer.

But don't misunderstand, Hagel has said.

"Not that I'm a pacifist -- I'm a hard-edged realist, I understand the world as it is -- but war is a terrible thing," he is quoted in the 2006 biography, "Chuck Hagel: Moving Forward."

"There's no glory," he said of war, "only suffering."