The cutbacks would be slated for fiscal year 2012 and would follow more than 20 programs that Defense Secretary Robert M. Gates terminated or truncated in April 2009, saving what the Pentagon estimated as more than $300 billion in long-term costs.

Those were “really, really tough decisions,’’ Admiral Michael Mullen, chairman of the Joint Chiefs of Staff, said in an interview during a taping of “Conversations with Judy Woodruff,’’ to be shown tomorrow on Bloomberg Television. “There will be more cuts.’’

“We’re going through that process,’’ Mullen said. “Programs from all the services which aren’t performing well, which can’t get themselves under control in terms of cost and schedule, they’re going to be looking at either being slowed down dramatically or being eliminated.’’

Defense accounted for about 55 percent of overall discretionary federal spending last year, so the military budget faces increased pressure, including from the National Commission on Fiscal Responsibility and Reform that President Obama created to identify tax and spending options to cut the deficit.

Yesterday, Representative Barney Frank, Democrat of Newton, released a letter from 57 representatives and senators that calls on the commission to consider substantial cuts in defense.

“Given the size of our deficit and debt problems as well as the political challenges and policy controversies involved in implementing any solutions to them, it is clear to us that cutting the military budget must be part of any viable proposal,’’ according to the letter signed by fellow legislators, including most of the Massachusetts House delegation.

One Republican, Representative Ron Paul of Texas, also lent his support.

A key debate among the commissioners on the deficit reduction panel is whether to safeguard defense spending from any proposal for reducing government expenditures. A growing number of lawmakers believe paring defense spending, which has doubled since 2001 to nearly $700 billion a year — including the costs of wars in Iraq and Afghanistan — must be part of any solution that brings the government’s ledger back into balance.

“Applying the adage that it is necessary to ‘go where the money is’ requires that rigorous scrutiny be applied to military spending,’’ the lawmakers wrote. “We believe that such an analysis will show that substantial spending cuts can be made without threatening our national security.’’

Frank, with Paul and other legislators, commissioned a study this year by the Cambridge-based project on Defense Alternatives that identifies ways to cut nearly $1 trillion from the defense budget in the next decade.

Mullen’s remarks are “an early indicator of what to expect’’ in the budget request for fiscal 2012, which starts next Oct. 1, said Todd Harrison, a budget analyst for the nonpartisan Center for Strategic and Budgetary Assessments in Washington.

“The Defense Department seems to be placing a greater emphasis on cost and schedule at the expense of performance,’’ he said. “This is in stark contrast to a decade ago, which placed a premium on improved performance with little regard to cost.’’

Bryan Bender of the Globe staff contributed to this report.