The top US military officer raised doubts Wednesday over the future of the costly F-22 fighter jet program, noting that the economic downturn could force the Pentagon to make budget cuts.

The Lockheed Martin/Boeing F-22 Raptor, conceived during the Cold War, is considered by its critics -- including Defense Secretary Robert Gates -- to be ill-adapted for use in irregular conflicts like Iraq and Afghanistan.

"It's important for all of us -- in the Defense Department too -- to squeeze our budgets, to draw in where we can," Chairman of the Joint Chiefs of Staff Admiral Michael Mullen told reporters at the Pentagon.

"I'm obviously discouraged by the lack of cost control that we've got in so many of our programs," Mullen said. "We are going to have to get a grip on that or we will not be able to buy them."

Concerning the F-22, "it's not a matter of, do we need it? We have it," said Mullen. "It's a question of, how many do we need for the future?"

"I am concerned that it is such an expensive system," he said, adding that the Air Force is seeking another 60 above the 183 F-22s they currently have.

The program has already cost more than 65 billion dollars -- each F-22 costs 350 million dollars.

Top US air force officials however defend the program by saying the fighter jets are well adapted for use against potential US rivals such as China.

Key members of Congress are also reluctant to end the program, as it is the source of thousands of jobs across the United States.

"I think ... in the aviation world, our future is in the Joint Strike Fighter," Mullen said.

He was referring to the Lockheed Martin F-35, designed to replace the F-16 fighter, widely used in the Air Force. But the program, which also involves several other countries, also suffers from delays and over costs.

The Pentagon plans to buy some 2,400 Joint Strike Fighters through 2027.