WASHINGTON — To hear the Republican leadership tell it, the once-sacred Pentagon budget, protected by the party for generations, is suddenly on the table. But a closer look shows that even as SpeakerJohn A. Boehner and Representative Eric Cantor, the House majority leader, insist on the need for military cuts, divisions have opened among Republicans about whether, and how much, to chop Pentagon spending that comes to more than a half trillion dollars a year.

Those differences were on display Wednesday on Capitol Hill, where the traditional Republican who now leads the House Armed Services Committee, Representative Howard P. McKeon, fought back against proposed cuts in the Pentagon budget even as fledgling committee members supported by the Tea Party said that the nation’s debts amounted to a national security risk.

“I cannot say it strongly enough: I will not support any measures that stress our forces and jeopardize the lives of our men and women in uniform,” Mr. McKeon said in an opening statement that followed up on a letter to Defense Secretary Robert M. Gates urging him not to stop work on the Marines‘ $14.4. billion Expeditionary Fighting Vehicle, a combined landing craft and tank for amphibious assaults that Mr. Gates canceled this month.

But Representative Chris Gibson, a Tea Party-endorsed freshman Republican and a retired Army colonel from New York’s Hudson River Valley, made it clear that no part of the Pentagon’s $550 billion budget — some $700 billion including the wars in Iraq and Afghanistan — was immune.

“This deficit that we have threatens our very way of life, and everything needs to be on the table,” Mr. Gibson told William J. Lynn III, the deputy defense secretary, who testified at the hearing along with Gen. Peter J. Chiarelli, the vice chief of staff of the Army, and other service vice chiefs.

The discordant Republican voices on military spending have bred confusion on Capitol Hill, among military contractors and within the military itself, where no one is exactly sure what the members backed by the Tea Party will do. It also shows why taking on the military budget will be so hard, even though a widening deficit has led the president and the leaders of both parties to say this time they are serious.