Nine Republican presidential hopefuls squared off in Iowa Wednesday in a rapid-fire short-answer battle that yielded a common theme: cut federal spending.

The Des Moines Register/Iowa Public Television debate held in Johnston, Iowa — the last GOP face-off before the Jan. 3 Iowa caucuses — came at a time when illegal immigration has emerged as a central theme in the Republican primary race. But the relatively tame debate glossed over the issue in favor of concentrating on economic questions.

In the opening exchange, former New York City Mayor Rudy Giuliani called for across-the-board federal spending cuts.

"We have to reduce government spending and we have to be very disciplined about that," he said. "And we have to do it by imposing spending caps on the civilian agencies and governments, 5 percent, 10 percent, maybe 15 percent."

He predicted savings of more than $20 billion through that and other steps. He also called for reducing corporate taxes and eliminating the estate tax.

Former Massachusetts Gov. Mitt Romney echoed the call for reining in government, but offered a more compromising tone.

"Surely, protecting our country and our defense of our military is critical; getting our free market finally able to allow all of our citizens to have insurance ... these are a lot of things that we can do, but they don't require us to eliminate the things that are most critical in our society," he said. "Instead, they require us to get rid of those things that are unnecessary. And the sacrifice that we need from the American people, it's this: It's saying let the programs that don't work go."

The debate barely touched on the hot button of illegal immigration as candidates tried to weave the issue into their responses. Romney and Giuliani each made a passing reference to his desire to end illegal immigration, while Colorado Rep. Tom Tancredo, who has made fighting illegal immigration the central theme of his campaign, addressed the issue most directly.

“Massive immigration is a problem," he said, adding that immigration without assimilation is a "catastrophe."

With several recent polls showing former Arkansas Gov. Mike Huckabee overtaking Romney in first place in Iowa, the debate posed an opportunity for his opponents to try to unseat the new frontrunner. But few candidates took any shots at Huckabee.

Romney at one point made a curt retort when Huckabee said he raised standards in education while governor.

"I just wanted a small adjustment to what Governor Huckabee had to say. And I don't believe you had the finest record of any governor in America on education," Romney said to Huckabee.

Tancredo chided Huckabee after the former governor stated his support for having music and art education in every school.

"Governor, with all due respect, you can't say on one hand you're against having government intervention, and on the other hand tell us that you want music and art and everything else in the school. That's not the job of a president. It is the job of a governor," he said.

At times, it seemed moderator Carolyn Washburn, editor of the Des Moines Register, was more the common enemy than Huckabee.

The debate momentarily broke into a bickering match when candidates were asked how many of them felt climate change was a serious threat.

“I’m not doing hand shows today,” former Tennessee Sen. Fred Thompson said. “You wanna give me a minute to answer that?”

Washburn responded no.

“Then I’m not gonna answer it,” Thompson said, prompting laughter and applause.

Ultimately, nobody strongly disputed global warming, but disagreed as to the primary cause.

"Climate change is real. It's happening. Human beings are contributing to it," Giuliani said.

Ariz. Sen. John McCain agreed, while Romney called for a global approach to the problem: "We call it global warming, not America warming."

Huckabee suggested the federal government take the lead role in using alternative forms of energy, in order to create a market for it and reduce climate change.

U.S. Ambassador Alan Keyes, who was permitted to appear in the debate, despite a late entry into the race and a zero register in polls, livened up the debate by answering every question with a return to his core theme of hypocrisy in government.

"Who represents the voice that they're absolutely determined to overlook in the discussion of our sovereignty and the betrayal of this people's sovereignty, on the border, on our moral principles, on the major export overseas -- which is our jobs? These folks represent the very elite who year, after year, after year, have destroyed our Constitution, betrayed our rights and undermined our strength created by our people in the world," Alan Keyes said, responding to the question on global warming.

"I agree with Alan Keyes' position on global warming," Thompson said to laughs.

"I'm in favor of reducing global warming," Keyes continued, "because I think the most important emission we need to control is the hot air emission of politicians who pretend one thing and don't deliver."

Giuliani at one point was put in the hot seat when asked about accusations that his administration in New York obscured security expenses related to trips he was taking during an extramarital affair to see Judith Nathan, who is now his wife.

"The reality is that all that information was available and known to people, known six years ago. And I would make sure that government was transparent. My government in New York City was so transparent that they knew every single thing I did almost every time I did," Giuliani said. "And on the issue of transparency, I can't think of a public figure that's had a more transparent life than I've had."

While the bulk of the debate was spent on economic issues, Washburn, who was roundly criticized afterward by focus groups asked to rate the candidates' performances, said she skipped over the issues of Iraq and immigration since many voters know where the candidates stand.

The first question of the debate specifically asked the candidates whether national debt threatens national security.

"I wouldn't call it national security. I would call it economic security," Giuliani said.

Huckabee said the debt absolutely is a national security threat, while Romney attempted to calm fears over the problem.

Romney said the future was not "bleak," but "bright," and said national leaders just need to reduce the growth in spending.

Asked if the nation should alter its trade policies with countries that commit human rights violations, several candidates used the question to defend free trade principles.

"America should think about free trade, a global economy as something we wanna embrace," Giuliani said, adding that the country needs to think about how to market to the millions of people coming out of poverty in countries like China and India — "these are new customers for the United States of America."

Thompson said: "I think free trade is the backbone of our economy."