General David Petraeus, one of the U.S. military's most influential voices, is warning against limiting the versatility and flexibility of the armed forces, as the Pentagon prepares to make drastic budget cuts.

Petraeus said Wednesday the government is facing “difficult budget decisions” but that the September 11 terrorist attacks in 2001 are a reminder that the military cannot always choose how, where, and when to fight its battles. He said this shows the armed forces need to maintain the “full-spectrum capability” that has been developed during the past decade of war in Afghanistan, Iraq, and elsewhere.

He also said the nation's leaders must remember that taking care of soldiers and their families remains a “paramount objective.”

The four-star general made the remarks as he steps down from the military after a nearly-four-decade career that included leading roles in the Iraq and Afghanistan conflicts. Petraeus will be sworn in as head of the CIA next week. Petraeus has said he chose to begin his new post as a civilian in order to preserve the distinction between the military and covert intelligence operations.

Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, praised Petraeus at the retirement ceremony, saying the general has reminded the U.S. that the right ideas under the right leadership can make “almost anything” possible.

Petraeus will succeed Leon Panetta, who became the U.S. defense secretary in July.