WASHINGTON  The chairman of the Senate Armed Services Committee on Tuesday declared that cost overruns for Defense Department weapons had “reached crisis proportions,” after government auditors reported that the projected final cost of the Pentagon’s major programs had ballooned $295 billion over initial budget estimates.

The chairman, Senator Carl Levin, Democrat of Michigan, also said that he would propose a law creating an independent director of cost assessment at the Pentagon. Mr. Levin said there was a need for stronger evaluation of whether contractors were making unrealistic promises to get programs started, ensuring later overruns and delays.

“It’s going to take a fundamental change in the structure and the culture of the acquisition system to address that problem,” Mr. Levin said at a committee hearing on the cost overruns.

Testifying before the committee, the Pentagon’s top procurement officer, John J. Young Jr., reserved judgment on Mr. Levin’s proposal, saying he needed more time to study it.