In this Dec. 10, 2008, file photo, Gen. David Petraeus, commander U.S. Central Command, arrives for a meeting at the U.S. Naval Forces Central Command in Manama, Bahrain. Petraeus, commander of U.S. forces in Iraq and Afghanistan, has told his troops that despite progress on both war fronts the U.S. and its allies face a tough fight in the year ahead. (AP Photo/Scott Olson, Pool)

U.S. Central Command Gen. David Petraeus speaks during an interview at a U.S. military base in Bagram north of Kabul, Afghanistan, Thursday, Nov. 6, 2008. A series of U.S. missile strikes in Pakistan's tribal areas in recent months has killed three of the top 20 extremist leaders there, causing a blow to insurgents threatening the nuclear-armed Pakistan's very existence, the top U.S. general in the region said Wednesday. (AP Photo/Rafiq Maqbool)

U.S. Central Command Gen. David Petraeus points as he talks with Afghan Defence Minister Abdul Rahim Wardak, unseen, after arriving at the ministry in Kabul, Afghanistan, on Wednesday, Nov. 5, 2008. (AP Photo/Rahmat Gul)

New head of the U.S. Central Command, U.S. Army Gen. David Petraeus, left, shakes hands with outgoing head U.S. Army Lt. Gen. Martin Dempsey, as U.S. Navy Admiral Mike Mullen, Chairman of the Joint Chiefs of Staff, looks on during Change of Command Ceremonies Friday morning Oct. 31, 2008 at MacDill Air force Base in Tampa, Fla. (AP Photo/Chris O'Meara)

New head of the U.S. Central Command, U.S. Army Gen. David Petraeus, right, U.S. Navy Admiral Mike Mullen, Chairman of the Joint Chiefs of Staff, second from right, Secretary of Defense Robert Gates, second from left, and outgoing Centcomm head U.S. Army Lt. Gen. Martin Dempsey, left, salute the colors during Change of Command Ceremonies Friday morning Oct. 31, 2008 at MacDill Air Force Base in Tampa, Fla. (AP Photo/Chris O'Meara)

A stiff breeze blows the flags from left, Florida, the United States, and the city of Tampa, during United States Central Command change of command ceremonies Friday morning Oct. 31, 2008 at MacDill Air force Base in Tampa, Fla. U.S. Army Gen. David Petraeus takes over command from U.S. Army Lt. Gen. Martin Dempsey. (AP Photo/Chris O'Meara)

New head of the U.S. Central Command, U.S. Army Gen. David Petraeus, left, shakes hands with outgoing head U.S. Army Lt. Gen. Martin Dempsey, as U.S. Navy Admiral Mike Mullen, Chairman of the Joint Chiefs of Staff, looks on during Change of Command Ceremonies Friday morning Oct. 31, 2008 at MacDill Air force Base in Tampa, Fla. (AP Photo/Chris O'Meara)

New head of the U.S. Central Command, U.S. Army Gen. David Petraeus covers his heart as troops applaud during change of command ceremonies Friday morning Oct. 31, 2008 at MacDill Air Force Base in Tampa, Fla. Petraeus takes over the command from U.S. Army Lt. Gen. Martin Dempsey. (AP Photo/Chris O'Meara)

New head of the U.S. Central Command, U.S. Army Gen. David Petraeus stumbles as he takes the stage during change of command ceremonies Friday morning Oct. 31, 2008 at MacDill Air Force Base in Tampa, Fla. Petraeus takes over command from U.S. Army Lt. Gen. Martin Dempsey. (AP Photo/Chris O'Meara)

In this Oct. 7, 2008 file photo, Gen. David Petraeus speaks at the Association of the United States Army annual meeting in Washington. (AP Photo/Manuel Balce Ceneta, File)