Nov. 29 (Bloomberg) -- Mitt Romney, who has been leading the Republican presidential race in early voting states, came under sharp attack from the other contenders on immigration and torture during last night's debate in Florida.

From the opening question, Romney and Rudy Giuliani exchanged barbs about their records regarding undocumented immigrants. Romney accused Giuliani, the former mayor of New York, of turning the city into a ``sanctuary'' for illegal immigrants. Giuliani said Romney operated a ``sanctuary mansion'' because illegal immigrants worked at his home.

``You were employing illegal immigrants,'' Giuliani, 63, said. ``That is a pretty serious thing.'' Romney, 60, the former governor of Massachusetts, countered that ``the policies of the mayor of pursuing a sanctuary nation or pursuing a sanctuary city are, frankly, wrong.''

The tone of the debate, sponsored by CNN, the Web site YouTube and the Republican Party of Florida, reflected the open nature of the Republican nomination race with a little more than a month before the Iowa caucuses and the New Hampshire primary.

As Giuliani and Romney focused on each other, former Tennessee Senator Fred Thompson criticized Romney and Mike Huckabee, the former governor of Arkansas who has risen in polls to contend for the lead in Iowa. Arizona Senator John McCain also took on Romney for refusing to classify waterboarding, or simulated drowning, as torture.

`High Ground'

``Well, Governor, I'm astonished that you haven't found out what waterboarding is,'' McCain, 71, a former prisoner of war in Vietnam, said. ``Governor, let me tell you, if we're going to get the high ground in this world and we're going to be the America that we have cherished and loved for more than 200 years, we're not going to torture people.''

On taxes, spending and social issues from abortion to gay rights and gun control, the candidates repeated their standard stump positions largely without engaging one another.

The subject of the Iraq war did spark sharp exchanges between McCain and Texas Representative Ron Paul, 72, the libertarian Republican who was the only candidate on the stage steadfastly opposed to the war.

McCain veered from a question about taxes to chastise Paul for his position. ``I've heard him now in many debates talk about bringing our troops home, and about the war in Iraq and how it's failed,'' McCain said. ``And I want to tell you that that kind of isolationism, sir, is what caused World War II.''

Use of Force

Paul responded that McCain ``doesn't even understand the difference between non-intervention and isolationism.'' Paul said he favored trade and travel, ``but I don't want to send troops overseas using force to tell them how to live.''

Illegal immigration is one of the top issues for Republican voters and it took up the most time of any single topic during the debate, which featured questions from the public recorded and posted to YouTube.

Giuliani was put on the defensive with the first question, from a New York man who said the former mayor had been ``aiding and abetting illegal aliens'' while in office.

Giuliani said that while the city didn't take action against undocumented immigrants who sent children to schools, reported crimes or sought emergency health care, local authorities ``reported thousands and thousands and thousands of names of illegal immigrants who committed crimes to the immigration service.''

That opened the exchange with Romney. ``The idea that they reported any illegal alien that committed a crime -- how about the fact that the people who are here illegally have violated the law?'' he said.

`A Serious Situation'

When asked about immigration, McCain said the evening's debate saddened him ``because we do have a serious situation in America.'' McCain, who supported the immigration overhaul legislation that failed in Congress earlier this year, said he would secure the borders while also recognizing that immigrants ``are God's children as well.''

Thompson, 65, pledged to veto any legislation that provided amnesty for illegal immigrants. ``A nation that cannot and will not defend its own borders will not forever remain a sovereign nation,'' he said, and then accused Romney of changing his position on the issue.

Under Attack

Huckabee, 52, also found himself under attack on the issue. One video raised his support for a proposal that would have allowed children of illegal immigrants who had gone through school in his state to apply for academic scholarships.

``He basically said that he fought for giving scholarships to illegal aliens,'' Romney said.

``In all due respect,'' Huckabee replied, ``we are a better country than to punish children for what their parents did. We're a better country than that.''

Huckabee also got one of the biggest laughs of the night when asked ``what would Jesus do'' with the death penalty. Said Huckabee: ``Jesus was too smart to ever run for public office.''

The debate itself generated controversy when it was discovered that one of the questioners has been a supporter of Senator Hillary Clinton, the front-runner for the Democratic nomination. Moderator and CNN anchor Anderson Cooper issued an apology after the network learned retired General Keith Kerr, who asked about Pentagon policy regarding gays in the military, was listed on a Clinton campaign press release issued six months ago as a member of a campaign support committee.

``Had we known that, it would have been disclosed by us,'' Cooper said.

Phil Singer, a spokesman for Clinton, said Kerr ``is not a campaign employee and was not acting on behalf of the Clinton campaign.''

To contact the reporters on this story: Kristin Jensen in Washington at kjensen@bloomberg.net; Catherine Dodge in Washington at cdodge1@bloomberg.net

Last Updated: November 29, 2007 17:09 EST