Defense leaders and members of Congress drew a line in the sand Thursday, saying the Pentagon must be spared from any budget cuts beyond an initial plan to slash at least $450 billion over the next 10 years.

The military, they said, must not take even deeper cuts _ a looming threat if lawmakers fail to agree on $1.2 trillion in federal budget savings by Thanksgiving and instead allow automatic cuts to kick in.

Defense Secretary Leon Panetta said President Barack Obama shares his view that the Pentagon should be shielded from any additional budget cutting.

Appearing before the House Armed Services Committee on Thursday, Panetta and Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, pounded home their message that further cuts would create national security risks and devastate the military.

"I don't say that as scare tactics, I don't say it as a threat, it's a reality," Panetta said. He said the initial $450 billion reduction will "take us to the edge" but any more than that would hollow out the force and "badly damage our capabilities for the future."

Despite questions from the committee members, Panetta and Dempsey provided no details on any planned spending cuts and they gave no specifics on how U.S. military strategy might be affected. They said they are still reviewing the issues.

The only new hint came when Dempsey opened the door for trimming the troubled F-35 fighter jet program. He told lawmakers that developing and building three versions of the F-35 Joint Strike Fighter _ one each for the Air Force, Navy and Marine Corps _ creates fiscal challenges for the department, and he suggested it may not be affordable.

During the early part of the hearing, eight protestors were arrested by Capitol police when they began shouting anti-war chants. Seven were charged with disruption of Congress and one was charged with simple assault.

During a news conference after the hearing, Republicans on the panel echoed the plea to spare defense from further reductions.

"We're saying: No more cuts," said Rep Howard "Buck" McKeon, R-Calif., the committee chairman.

And Rep. Mac Thornberry, R-Texas, highlighted Panetta's statement earlier that Obama shares his view that there should be no further cuts.

"I think it's important for the president as commander in chief to make his views known," Thornberry said. He said it's a message that congressional Democrats need to hear.

During the hearing, Panetta urged Congress to consider cuts to mandatory federal spending programs and increases in revenues in order to meet the deficit reduction plan.

Rising deficits and deep debt have forced the federal government to slash spending _ even at the Pentagon, whose budget has nearly doubled to some $700 billion in the 10 years since the Sept. 11 terror attacks.

The debt accord reached this past summer between Obama and congressional Republicans calls for a $350 billion cut in projected defense spending over 10 years. The Pentagon and House committee members say the actual number is more than $450 billion. The difference depends on the budget baseline that is used.

Panetta said the military has been stressed by a decade of fighting, squeezed by rising personnel costs, and is in need of modernization. In the last decade the military has focused heavily on fighting insurgencies and terrorists in Iraq and Afghanistan, rather than on the skills and equipment needed to fight modern armies, navies and air forces.

Meanwhile, international security issues have grown more complex, Panetta said, noting the United States must be prepared to continue dealing with violent extremists as well as the nuclear ambitions of Iran and North Korea, the prospects of cyber attackers who may target American infrastructure, and other threats.

Panetta also repeated the warning he issued earlier this week _ saying that some lawmakers' favored defense programs could be on the chopping block.

Recalling his time as a member of the U.S. House, Panetta noted that a military base in his district was cut in 1994.

"I lost Fort Ord. ... That represented 25 percent of my local economy. So I know what it means to go through this process," he said. "We have to do this right, and we can do it right."

If the special bipartisan deficit-reduction supercommittee fails to come up with at least $1.2 trillion in cuts from all federal spending by Thanksgiving, defense could face additional reductions. If the panel fails to come up with a proposal, or Congress rejects its plan, automatic cuts of $1.2 trillion kick in, with half of that to come from defense.

Panetta said the Pentagon is taking a comprehensive look at its spending, from overhead costs to the size of the force as the wars in Iraq and Afghanistan wind down, from modernizing weapons to personnel.

Rep. Adam Smith of Washington state, the top Democrat on the House panel, said in a recent interview that it would be wise for the Pentagon to provide details on its strategic review as Congress considers spending cuts.

"I urge them to get it out sooner," Smith said. "We're already deep into" the next budget.

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Associated Press writers Donna Cassata and Pauline Jelinek contributed to this report.