Texas Gov. George W. Bush clashed here tonight with Arizona Sen. John McCain over campaign finance reform and how to spend the federal surplus. But Bush passed up an invitation to criticize his leading rival for intervening before a federal agency on behalf of a wealthy campaign contributor.

With McCain on the defensive over his recent actions before the Federal Communications Commission, Bush refused to be drawn into the controversy, telling the Arizona senator, "I trust your integrity, I trust your judgment." But he immediately pivoted to attack McCain on the centerpiece of his candidacy, a campaign finance reform opposed by most of the GOP's elected leadership.

"It is bad for Republicans and it's going to hurt the conservative cause," Bush said.

In the first GOP debate of the new year, the six presidential candidates engaged in a series of rollicking exchanges as the hour-long session sometimes veered close to running out of control. The candidates argued over tax reform, gays in the military, the fate of young Cuban Elian Gonzalez and the role of religion in the Oval Office.

In New Hampshire, where the tax issue is a presidential perennial, Bush was challenged to promise that he would never raise taxes. His father, former President George Bush, was hurt in 1992 by having broken a "no new taxes" pledge that he made while campaigning four years earlier in this state.

Tonight, Bush said: "This is not only 'no new taxes,' this is 'tax cuts, so help me God.' "

The debate was sponsored by New Hampshire Public Television, New England Cable News and the Manchester Union Leader and was moderated by NBC's Tim Russert. The participants also included magazine publisher Steve Forbes, former Reagan administration official Gary Bauer, former diplomat Alan Keyes and Utah Sen. Orrin G. Hatch.

A group of Republican and Republican-leaning independents who watched the debate with Washington Post reporters gave their highest mark to Hatch, finding him more impressive than either McCain or Bush. The Arizona senator was judged by almost everyone in the group, including those who said they had been inclined to support him, to have had "a bad night."

Bush drew mixed grades, with some praising him for "directness" in his answers, while others said he appeared to be parroting lines from his TV ads and dwelling too much on his claimed accomplishments in Texas.

Bush came under sustained criticism from all five of his rivals, but in contrast to earlier debates, he responded repeatedly and aggressively. "Unlike other people on this stage who talk the talk, I have walked the walk," he said, adding, "I've got a record of accomplishment."

McCain also found himself on the defensive with the first question he received. Last month he urged the FCC to hold a long-delayed vote on the purchase of a Pittsburgh television station by a major contributor to his presidential campaign. McCain was asked if that was an example of hypocrisy or bad judgment.

No, he asserted, saying he would "do the same thing" again under similar circumstances. "People deserved to know the answer. . . . I think that's appropriate in my role as chairman" of the Senate Commerce Committee.

McCain has spent the past two days answering questions about the issue, which has called into question his image as a politician determined to break the link between money and influence in Washington. But while defending himself tonight, he acknowledged that he had canceled a weekend fund-raiser at the home of the contributor, television magnate Lowell Paxson, because "I knew that if I didn't that we'd be talking about that most of the time."

The Bush-McCain argument over campaign finance brought a testy exchange between two candidates who in the past have been completely civil toward each other. "I don't think you have an idea of how important campaign finance reform is to restore the confidence of young Americans in their government," McCain said.

"What you don't need to do is tell me what I have an idea about," Bush retorted.

McCain and Bush also sparred over the projected budget surpluses, with McCain repeating his charge that the governor's tax cut plan would squander the surpluses without protecting Social Security. McCain said he would set aside 63 percent of the surplus to strengthen Social Security and also "pay down the debt" before offering a massive tax cut.

"Here's my problem with that kind of Washington mind-set," Bush said. "It is a huge leap of faith to assume that Congress will not spend the money."

Bush's rivals jumped on him throughout the debate over his conservative credentials on taxes and other issues. Forbes charged that Bush had signed an anti-tax pledge in Texas and later broke it. Calling Bush's tax plan "Clinton Lite" and not real reform, Forbes said taxpayers would have to go through too many "hoops and loops" to know whether they got a real tax cut under the proposal.

Forbes's criticism of Bush was a prelude to a television ad that he will begin airing in New Hampshire on Friday, accusing the Texas governor of breaking his pledge not to support sales or business tax increases.

Bauer challenged Bush on his commitment to social and cultural issues of importance to conservative Republicans. "Why should GOP conservatives and voters believe that you will seriously defend our values in Washington, D.C., against that liberal establishment?"

Bush responded with a list of conservative issues he has supported in Texas. Then he added emphatically, "What Republicans need to do is elect somebody who has gotten results, tangible results that people can see, that people can put their arms around and say, 'This man's a leader.' "

Bush was called on to explain an answer he gave in a debate last month in Iowa, when he called Jesus Christ the most influential philosopher in his life. Should members of other faiths and non-believers feel excluded by his beliefs? "No," Bush answered. "I was asked what influenced my life and I gave the answer." He added that his belief "doesn't make me better than you or make me better than anybody else, but it's a foundation for how I live my life."

Asked if he would take a "what would Jesus do" approach to governing, he said, "I would take an expression into the Oval Office of 'Dear God, help me.' "

Bauer replied, "So would we, Governor."

"Now that wasn't very Christian of you," Bush responded.

All the candidates criticized Democrats Al Gore and Bill Bradley for saying in Wednesday's debate that they would insist that members of their Joint Chiefs of Staff agree with a policy of allowing gays to serve openly in the military. Bauer called Gore's statement "one of the most idiotic answers I've ever heard."

But the Republicans disagreed over whether they would continue the policy of "don't ask, don't tell," supported by Bush and McCain, or bar homosexuals from serving at all. Keyes decried the "radical homosexual agenda" and vowed to "return the ban on homosexuals in the military" if he becomes president.

Keyes drew a concession from McCain over an issue of popular culture. He attacked McCain for calling "Nine Inch Nails" his favorite musical group during a recent interview, saying McCain was "aiding and abetting the cultural murder" of young people by promoting a group that records filthy lyrics. McCain, noting that he had seen such performers as Puff Daddy, Busta Rhymes and the Backstreet Boys at a recent MTV awards show, said he was trying to be "amusing and entertaining" in that interview. "It was a poor choice," he said.

Keyes agreed: "I'm a father and I'm not laughing, I'm really not."

The future of Elian Gonzalez produced spirited condemnations of Cuba's Fidel Castro. "Fidel Castro ought to butt out," Hatch said, but he added that U.S. politicians ought to stay out of the case as well. "Let's do what's best for the child."

Three earlier Republican debates have been fairly dry affairs, but the one here was a donnybrook. The candidates joked, jibed, interrupted, shouted, digressed. At one point, Keyes dressed down moderator Russert.

Forbes was asked at one point to "open up" about his struggling candidacy to prove to voters that he was not aloof or out of touch. "Maybe you want me to give a hug to John," he answered, referring to McCain. "I'd be glad to, Steve," McCain said--and then stepped toward Forbes with arms extended.

Staff writers Terry M. Neal and Ben White contributed to this report.