WASHINGTON – Republican presidential candidates grappled Tuesday over how to balance civil liberties and security, as they engaged in a lively and substantive debate over how best to protect Americans from threats around the world.

With the Iowa caucuses, the nation's first political test of 2012, only six weeks away, the eight GOP hopefuls clashed over how to address U.S. trouble spots from Pakistan to the Mexican border.

The debate, co-sponsored by CNN and two conservative policy-research centers, the American Enterprise Institute and the Heritage Foundation, was the first in 10 days and the first since former House Speaker Newt Gingrich vaulted to the top in several national polls.

The candidates generally refrained from criticizing one another sharply. Instead, they politely but aggressively clashed over how to restrain Iran, after the United States and its allies Monday increased financial pressure on Iran with new sanctions on that nation's central bank and energy sector.

"We need a strategy of defeating and replacing the current Iranian regime with minimum use of force," Gingrich said.

Texas Gov. Rick Perry insisted the United States needs tougher sanctions against the Iranian central bank.

"That will shut down the economy," he said.

Some candidates offered contrasting views on Afghanistan. President Barack Obama plans to bring the "surge" troops home by September 2012 and all troops by 2014.

Former Utah Gov. Jon Huntsman wanted a more accelerated drawdown, and Texas Rep. Ron Paul questioned why U.S. troops are there at all.

Former Massachusetts Gov. Mitt Romney, though, said the surge troops should not be wound down until December 2012.

"This is not time for America to cut and run," he said.

Romney said his stand on Afghanistan was based on the advice of military commanders. But, reminded Huntsman, "the president is the commander-in-chief and ought to be informed by a lot of different voices, including those of his generals on the ground."

Romney was staunch when the topic shifted to Israel.

"My first foreign trip will be to Israel to show the world we care about that country and that region," he vowed.

Candidates were asked if they would help Israel if it attacked Iran, in order to stop Iran from developing nuclear weapons.

"If Israel had a credible plan that it appeared as if they could succeed, I would support Israel, yes," businessman Herman Cain said.

Paul was wary and animated.

"We don't even have a treaty with Israel," he said. "Why do we have this automatic commitment that we're going to send our kids and send our money endlessly to Israel?"

When the topic turned to Pakistan, Perry was the skeptic.

"Until Pakistan clearly shows that they have America's best interests in mind, I would not send them one penny, period," he said.

That's "highly naive," Rep. Michele Bachmann of Minnesota shot back. "They certainly aren't looking out for the best interests of the United States. I wouldn't expect them to."

The best way to engage with an "uneven actor," she said, is to "have some sort of presence there."

Gingrich tried a more comprehensive approach to Afghanistan and Pakistan.

"You want to keep American troops in Afghanistan, you accept hot pursuit, you say no sanctuaries, you change the rules of engagement, you put the military in charge of the military side, you overhaul the State Department and AID (Agency for International Development) so they get the job done, and you do it for real and you do it intensely," he said.

And, he added, "You tell the Pakistanis: Help us or get out of the way, but don't complain if we kill people you're not willing to go after on your territory, where you have been protecting them."

The night's starkest differences involved the Patriot Act, the law passed in the aftermath of the 2001 terrorist attacks that gave the government powers to spy on and combat suspected terrorists.

Most of the candidates agreed that being prepared to stop a terrorist attack requires extraordinary measures and that terrorist suspects do not deserve the same rights guaranteed by the Constitution to suspects of domestic crimes.

"We don't give Miranda rights to terrorists," said Bachmann.

Paul and Huntsman disagreed, arguing that Americans are giving up precious personal freedoms out of fear of terrorism.

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