ABC News’ Huma Khan and Sunlen Miller report: As calls to slash the federal budget grow louder, Defense Secretary Leon Panetta warned today that hefty cuts in the nation’s military budget that go beyond the $450 billion already planned could have devastating consequences.

“I’m not kidding you. When you cut the budget by $450 billion, when you make the choices you have to make, there are some risks that are out there,” Panetta told members of the House Armed Services Committee.

But both Panetta and Chairman of the Joint Chiefs of Staff Martin Dempsey acknowledged that changes can be made to the way the Pentagon works. Panetta, who recently took over the reins from Robert Gates, said he is calling for the agency to cut in half the time it will take to achieve audit readiness for the statement of budgetary resources. The Defense Department is one of only two major agencies that has never had a clean audit opinion on its financial statements, Panetta said.

Dempsey also expressed less enthusiasm for the F-35 joint strike fighter program, saying that creating three versions of the new, fifth-generation fighter jet could be financially burdensome for the agency.

Sen. John McCain, R-Ariz., echoed Panetta’s concerns about further cuts in defense and took them one step farther, saying he would work to nullify the cuts that would be triggered automatically if a deficit supercommitee created in the deal to avert a government shutdown this summer fails to act.

The $500 billion in automatic Defense Department cuts would be triggered if the Senate supercommittee’s recommendations aren’t taken up. They would come on top of the already $450 billion the Department of Defense has to cut over the next decade.

“My reaction is that if there’s a failure on the part of the supercommittee that we will be amongst the first on the floor to nullify that provision,” McCain said at a news conference with other Republicans today. “The Congress is not bound by this. It’s something we passed, we can reserve it. And I agree with him.”

Asked what the point of the trigger was, as negotiated in the debt ceiling compromise, if legislators could just overturn them, McCain said, “I didn’t agree with the trigger being created to start with. So I have no ownership in that. But so the fact is that we cannot, as Secretary Panetta said, afford to have those additional cuts to the $480 billion.”

With grassroots groups such as the Tea Party calling on lawmakers to cut spending, the defense budget has taken center stage in the 2012 debate. Most conservatives oppose hefty cuts to the military but not all are on the same page.

“My choice is not to cut defense. I think it’s a terrible idea to cut defense,” GOP presidential candidate Mitt Romney said Tuesday night at the Republican debate.

The former Massachusetts governor supports higher defense spending, telling veterans last week that he’d like to see the defense budget be about 4 percent of the economy, compared to 3.8 percent currently.

Rep. Michele Bachmann, R-Minn., has voiced similar sentiments.

“Defense spending is not the culprit when it comes to our nation’s debt like some want you to believe,” the GOP presidential candidate wrote in a blog in May.

Tea Party darling Herman Cain, however, has adopted a more cautious approach. Amid calls from Tea Partiers for hefty budget cuts, the former chief executive of Godfather’s Pizza has said he would have to review military programs before deciding whether its budget should be slashed.

“Until I have access to that information about what those programs are, I’m not going to say that I’m going to cut defense spending. It’s on the table. But the world is not safer,” the GOP presidential candidate told CBS News in June.

Today’s hearing got off to a rocky start as anti-war protestors continually disrupted Panetta’s opening testimony. Eight demonstrators affiliated with anti-war group Code Pink were arrested, according to U.S. Capitol Police.

ABC News’ Luis Martinez and John Parkinson contributed to this report.