(Chip Somodevilla — Getty Images)

Gen. James F. Amos, Marine Corps commandant, told the House Armed Services Committee that the planned reductions would make it impossible, in the case of a major contingency, to rotate units in and out of a war zone. Marines would have to remain in place until they were no longer needed, Amos said.

The chiefs also described to the panel some of the risks the nation would face if further budget cuts were imposed. Should a special bipartisan congressional committee fail to reach agreement on cuts in federal spending, additional reductions would be applied in an across-the-board fashion. As Adm. Jonathan W. Greenert, chief of naval operations, put it: “The current law does not allow the military to manage these reductions, but rather applies the cuts uniformly to each program, project and activity.”

Greenert said the Navy’s readiness and procurement accounts would require an 18 percent cut. Although the law would not affect the fiscal 2012 budget, such reductions would require the Navy to cut programs and personnel to begin 2013 at levels specified under the law.

The Army, which plans to reduce its active forces but keep or increase the size of the Reserves and National Guard, would instead face “significant reductions” in the size of both those elements, its chief of staff, Gen. Raymond T. Odierno, told the panel. The Air Force, in the same circumstances, would have to retire some 1,000 aircraft and lose 10,000 people, according to Gen. Norton A. Schwartz, Air Force chief of staff.

Wednesday’s hearing continued a series the committee has held over the past month to publicize concerns of the Republican majority that too much of the budget reduction program already underway is harming national security.

In opening the session, the committee chairman, Rep. Howard P. (Buck) McKeon (R-Calif.), said: “The problem is that to date, defense has contributed more than half of the deficit reduction measures we’ve taken and there are some who want to use the military to pay for the rest, to protect the sacred cow that is entitlement spending.”