JOHNSTON, Iowa — The subdued Republican debate today belied the fierce, increasingly negative battle in Iowa and elsewhere for the party’s presidential nomination.

The candidates largely held their fire in their final meeting before the state’s January 3 leadoff caucuses, mindful that negative campaigning can backfire, particularly in Iowa.

“Let’s raise the level of dialogue and discussion and debate in this campaign,” Senator McCain proposed, well into a 90-minute debate remarkably free of acrimony.

Offstage, the GOP race has turned sharply contentious.

In Iowa, religion and immigration are dominating the campaign three weeks before the state’s caucuses. With polls showing a dead heat, Mitt Romney and Michael Huckabee have squared off daily on both issues.

Mr. Romney, a former Massachusetts governor, started running a TV ad this week — the race’s first negative commercial — accusing Mr. Huckabee, a former Arkansas governor, of being soft on illegal immigration. Mr. Huckabee, for his part, invoked Mr. Romney’s Mormon faith in an interview. The ordained Southern Baptist preacher asked: “Don’t Mormons believe that Jesus and the devil are brothers?”

But none of that was raised in the debate, and the nine men on the stage were on their best behavior. Most passed up multiple opportunities to go after each other, instead restating their positions on everything from trade to taxes.

In part, the bland tone was the consequence of sober questions focused on the economy and the like, as well as a format, and moderator, that didn’t encourage direct confrontation. The candidates also were aware of the lesson learned in the 2004 Democratic race — Iowans don’t like political attacks.

The result: a debate that didn’t live up to its potential to be a defining point in the race.

“This is going to be forgotten,” a Republican who managed Bob Dole’s 1996 campaign, Scott Reed, said. “For the guys in the front, Huckabee and Romney, it was a good day. It didn’t do anything to shatter their standing.”

Added a GOP strategist unaligned in this race, Ed Rogers: “It was the last game of the season, so you would have thought it would be exciting and some people would make some big, trick plays. But no. I’m surprised.”

The subject of education produced the only semblance of sparks.

Moments after Mr. Huckabee said schools should provide all students with music and art instruction at all grade levels, Rep. Tom Tancredo of Colorado took him to task. “That’s not the job of a president. It’s the job of a governor,” he said. “That’s what you should run for if you want to dictate curriculum.”

Mr. Huckabee responded by saying that in his decade as governor he had the “most impressive education record.”

That brought a polite disagreement from Mr. Romney. “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 American on education,” he said, eliciting laughter from the debate audience.

Indeed, Arkansas public school students scored at or below the national average in four federal education test categories in 2007; Massachusetts public school students scored first in all areas, math, and reading for both 4th graders and 8th graders.

A couple of candidates did manage to throw some elbows.

A former Tennessee senator, Fred Thompson, used his answer on taxes to poke a rival worth between $190 million and $250 million: “My goal is to get into Mitt Romney’s situation, where I don’t have to worry about taxes anymore.” When Mr. Romney took issue with the comment, Mr. Thompson, a TV and film actor, shot back: “Well, you know, you’re getting to be a pretty good actor.”

Mr. McCain, assailed in corn-growing Iowa for his opposition to ethanol subsides, all but called his rivals fakes, saying: “I don’t believe that anybody can stand here and say that they’re a fiscal conservative and yet support subsidies” that hurt the American economy.

The editor of The Des Moines Register and the debate moderator, Carolyn Washburn, brought about a mini-revolt at one point when she asked all the candidates to raise their hands if they thought global warming was a serious threat caused by human behavior. “I’m not doing hand shows today,” Mr. Thompson said. “You want to give me a minute to answer that?”

“No, I don’t,” Ms. Washburn said.

“Well, then I’m not going to answer it,” Mr. Thompson said as Mayor Giuliani, Mr. McCain, and others talked over one another.

Ultimately, no one disputed global warming was a problem or that humans at least contribute to it.

For a change, a conservative commentator, Alan Keyes, was included in the debate. Virtually absent from the campaign trail, he kept pleading for equal time.

At one point, Mr. Giuliani defended himself over security expenses being charged to obscure city offices as he began his extramarital affair with his now-wife Judith.

“My government in New York City was so transparent that they knew every single thing I did almost every time I did,” Mr. Giuliani said. “I can’t think of a public figure that’s had a more transparent life than I’ve had.”

That comment provided an opening for any one of his rivals, yet none seized it.

In short, nobody wanted to be the Grinch — at least not in a televised debate in Iowa, the land of nice, just weeks before the caucuses and in the midst of the holiday season.