To make ends meet, Mr. Gates also announced that he would seek to recoup billions of dollars by increasing fees paid by retired veterans under 65 for Defense Department health insurance, even though Congress has rejected such proposals in the past. And he outlined extensive cuts in new weapons.

Cutting up to 47,000 troops from the Army and Marine Corps forces  roughly 6 percent  would be made easier by the withdrawal under way from Iraq, and the reductions would not begin until 2015, just as Afghan forces are to take over the security mission there. But Mr. Gates said the cuts in Pentagon spending were hardly a peace dividend, and were forced by a global economic recession and domestic pressures to find ways to throttle back federal spending.

“This department simply cannot risk continuing down the same path where our investment priorities, bureaucratic habits and lax attitudes toward costs are increasingly divorced from the real threats of today, the growing perils of tomorrow and the nation’s grim financial outlook,” Mr. Gates said at an afternoon news conference.

The president’s budget for the 2012 fiscal year, which is due by mid-February, would freeze discretionary spending, but that would not apply to military, veterans and Homeland Security programs. Last fall, a majority of the members of Mr. Obama’s bipartisan National Commission on Fiscal Responsibility and Reform, including three Republican senators, said military spending also should be reduced as part of a long-term debt-reduction plan.

The Pentagon’s proposed operating budget for 2012 is expected to be about $553 billion, which would still reflect real growth, even though it is $13 billion less than expected. The Pentagon budget will then begin a decline in its rate of growth for two years, and stay flat  growing only to match inflation  for the 2015 and 2016 fiscal years. (The Pentagon operating budget is separate from a fund that finances the Afghanistan and Iraq wars.)