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Associated Press
Republican presidential candidates from left, former Massachusetts Gov. Mitt Romney, businessman Herman Cain, former House Speaker Newt Gingrich, and Rep. Michele Bachmann, R-Minn., applaud on stage before a Republican presidential debate in Washington, Tuesday, Nov. 22, 2011. (AP Photo/Evan Vucci)

WASHINGTON — Republican presidential hopefuls warned in near unanimity against deep cuts in the nation's defense budget Tuesday night, assailing President Barack Obama in campaign debate but disagreeing over the extent of reductions the Pentagon should absorb to reduce deficits and repair the frail U.S. economy.

The debate ranged widely, from Iran's threat to develop a nuclear weapon to the anti-terror Patriot Act, the war in Afghanistan, U.S-Pakistan relations and illegal immigrants who have entered the U.S. across the Mexican border. Former House Speaker Newt Gingrich said some should be allowed to stay, drawing fire from rivals Mitt Romney and Michele Bachman.

On defense spending, former Massachusetts Gov. Romney said nearly $1 trillion in cuts are on the horizon for the Pentagon over the next decade, noting that is the same as the costs for the nation's new health care law. He blamed Obama for that, adding, "We need to protect America and protect our troops and our military and stop the idea of Obamacare."

Texas Gov. Rick Perry was harshly critical of the magnitude of potential cuts saying the Obama administration's Pentagon chief had called them irresponsible. "If Leon Panetta is an honorable man, he should resign in protest," Perry said.

Neither Perry nor Romney specified if they support any cuts in the Pentagon's accounts, but Gingrich and Jon Huntsman, one-time ambassador to China, both indicated the topic should be on the table as budget-cutters look for savings.

"It's clear that there are some things you can do to defense that are less expensive," said Gingrich.

Only Rep. Ron Paul of Texas sounded unperturbed, saying that despite ominous talk, lawmakers are considering only reductions in future military growth, not actual cuts.

In a race constantly in flux, the former House speaker has recently emerged as Romney's principal rival atop the public opinion polls. As he looked around him, he saw other rivals who once held that position — Bachmann, Perry and businessman Herman Cain among them.

They and the other GOP would-be commanders-in-chief made their points in a national security debate a mere six weeks before the Iowa caucuses begin the formal competition for delegates to next summer's National Republican Convention. The venerable DAR Constitution Hall was the site — a few blocks from the White House and as close as most if not all of the GOP hopefuls are likely to get.

On immigration, Gingrich said that while some who are in the country illegally should be forced to leave the country, that wasn't true for all of them.

"If you've been here 25 years and you got three kids and two grandkids, you've been paying taxes and obeying the law, you belong to a local church, I don't think we're going to separate you from your family, uproot you forcefully and kick you out," he said.

Romney and Minnesota Rep. Bachmann strongly differed.

She said, "I don't agree that you would make 11 million workers legal, because that, in effect is amnesty."

Neither the format nor the moderator permitted all eight candidates to answer any one question, producing a somewhat disjoined event in which there was relatively little back-and-forth among the rivals.

Syria was one exception — Perry saying he supported a no-fly zone over the nation where President Bashir Assad's forces are using force to quell protests, and Romney saying now is not the time.

The focus on defense cuts came one day after Congress' supercommittee failed to reach agreement on a plan to reduce red ink by $1.2 trillion over the next decade, an outcome that threatens to trigger a similar amount in automatic spending cuts beginning in 2013.

The Pentagon's share of those reductions would be about $500 billion, an amount that would come on top of Obama's own plan to trim military costs by about $450 billion.