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 Speaker John A. Boehner and Rep. 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, Rep. 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," 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 Gates canceled this month.

But Rep. Chris Gibson, a Tea Party-endorsed freshman Republican and retired Army colonel from New York’s Hudson River Valley, made 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," 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 chiefs.

The cacophony of Republican voices on military spending has 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.

Most Tea Party candidates spoke little about national security and the military in fall political campaigns focused on cutting spending overall.

"It’s a mystery to me," Chiarelli said during a break in Wednesday’s hearing, then said he was eager to sit down at the Pentagon for talks with the newcomers.

McKeon, for one, is concerned, and so has quietly been meeting with the new members — a number have no prior experience in government — to educate them in national security. One congressional staff member who closely monitors the military said, "While McKeon would say that all members are entitled to advocate for positions they want to advocate, what he has been doing is working to educate new members on what the threats are, and why we need the defense budget close to where it is." The staff member asked for anonymity to discuss McKeon’s private meetings.

This month Gates announced plans to cut military spending by $78 billion over five years, the first serious proposed reductions in the budget since the Sept. 11, 2001, attacks and a response to White House pressure to squeeze spending during what Gates called a time of "extreme fiscal duress." But the Pentagon’s operating budget for 2012 is expected to be about $553 billion, which would still reflect real growth. The growth would slow over the next years and then stop by the 2015 fiscal year.

Dick Armey, a former Republican House majority leader and now a leader of the Tea Party movement, said in an interview that Tea Party-backed members of Congress would rigorously look for places to prune the Pentagon budget.

"A lot of people say if you cut defense, you’re demonstrating less than a full commitment to our nation’s security, and that’s baloney," he said.

So far, few Tea Party-backed members on the House Armed Services Committee have said specifically where they would cut. In public remarks at the hearing Wednesday, several spoke up in favor of favorite military programs or of protecting military installations at home, illustrating the difficulty of balancing overarching philosophy and goals with the immediate concerns of their districts.

McKeon, who represents a California district that is home to major defense contractors, was the single biggest recipient in the House of campaign contributions from military aerospace companies and their employees.

In an interview, Rep. Vicky Hartzler, a freshman Missouri Republican backed by former Gov. Sarah Palin of Alaska, said that her priorities were jobs and "reining in runaway spending." But when asked about the Pentagon budget, Hartzler, who defeated former Rep. Ike Skelton, the longtime Democratic chairman of the Armed Services Committee, said that "now is not the time to talk about defense cuts while we are engaged in two theaters with men and women in harm’s way."

Hartzler said she questioned the $78 billion in cuts to the military budget over the next five years and added, "I will be a staunch defender of military installations in my district and across the country."

Hartzler’s district has two large military bases, Fort Leonard Wood and Whiteman Air Force Base, home to the B-2 stealth bomber and a new ground-control station for unmanned Predator drones.

Rep. Scott Rigell, a Republican newcomer from Virginia who at first sparred with the Tea Party but then signed a pledge supporting many of its positions, said that he, too, was committed to strong military spending. In an interview after the hearing, he said that "as a very first priority, it is our constitutional duty to stand an army."

Rigell said he supported in the Pentagon budget "any responsible, wise reduction that can clearly be identified as waste," but needed more specific information before he could judge where to cut. His son, he said, is a member of the Marine reserve and drives an amphibious assault vehicle, an earlier version of the Expeditionary Fighting Vehicle. On Gates’ decision to eliminate the EFV, Rigell said, "The abruptness of the decision is concerning me because we went down a long, long path. We went from it being a good decision and people defending it to ‘it must be cut."’

Rigell, who represents a district around Virginia Beach that is economically dependent on the military installations, spoke at the hearing against Pentagon plans to move one of five nuclear aircraft carriers based in Norfolk to Mayport, Fla., taking with it 10,000 jobs.