GOFFSTOWN, N.H. — The leading Republican candidates debating at St. Anselm College here last night came across as sober men talking about serious issues.

Mayor Giuliani hit his stride early and performed well overall. His succinct and unequivocal response on a question about whether — given what we know now — invading Iraq was a mistake damaged Governor Romney, who gave a glib and intellectually consistent yet unsatisfying answer.

Mr. Romney gave a lawyerly response, calling it a “null set kind of question” because Saddam Hussein refused to allow weapons inspectors into Iraq, preventing us from acquiring adequate information. Mr. Romney is a skilled and fluid debater, but he can sometimes seem too cute by half.

Mr. Giuliani, who got to answer next, exploited that impression by saying, “Absolutely the right thing to do. It’s unthinkable that you would leave Saddam Hussein in charge of Iraq and be able to fight the war on terror.” He added: “Iraq should not be seen in a vacuum. Iraq is part of the overall terrorist war against the United States.”

Early in the debate, Mayor Giuliani articulated the central difference between his campaign and the Democrats with the possible exception of Senator Clinton. Citing the break-up of recent terror plots at John F. Kennedy Airport over the weekend and Fort Dix several weeks ago, Mr. Giuliani said, “These are real problems. This war is not a bumper sticker. This war is a real war.”

Technical problems plagued the debate. In the beginning, a jarring buzz interfered with the audio feed — a circumstance CNN commentator Wolf Blitzer blamed on bad weather. Later, significant portions of the candidate’s comments were inaudible inside the hall. Mayor Giuliani turned one audio miscue into a positive. Asked about a Roman Catholic bishop’s opposition to his position on abortion, Mr. Giuliani answered, but his response did could not be heard. Pointing toward the heavens, Mr. Giuliani said, “Look, for someone who went to parochial schools all his life, this is a very frightening thing that’s happening right now.”

While this moment wasn’t quite Ronald Reagan saying “I paid for that microphone” at a New Hampshire debate in 1980, an event credited with leading to his victory over George H.W. Bush, it nonetheless allowed Mr. Giuliani to display an ease with himself that had been missing at the last debate in South Carolina over the same abortion question.

During the question-and-answer session of the debate, Senator McCain at times seemed to be missing a step. But even in a somewhat clunky performance, Mr. McCain did have one transcendent moment when questions from the audience were allowed. A poised young woman, Erin Flanagan, whose brother is one of the military’s “best of the best,” asked the candidates what they would do in managing the conflict to allow the troops to be brought home.

Rep. Duncan Hunter got the question first and answered well, mentioning his son, who has fought in Iraq. Senator Brownback used the question to promote his plan for a three-state solution in Iraq.

Mr. McCain, with the weight of his own personal history behind him, rose from a chair and walked forward on the stage to address Ms. Flanagan directly. Several other candidates, including Mr. Giuliani, subsequently followed Mr. McCain’s lead in getting up out of their chairs.

“We are proud of you and your endurance, and we’re proud of your sacrifice,” Mr. McCain said. “I believe we have a fine general. I believe we have a strategy which can succeed, so that the sacrifice of your brother would not be in vain, that a whole 20 million or 30 million people would have a chance to live a free life in an open society and practice their religion, no matter what those differences are.”

It’s possible that Mr. McCain’s day may have passed and that the Iraq issue weighs him down too heavily. But no other moment exemplified Mr. McCain at his best.

Mr. Romney had a good moment when an audience member asked him about his Spanish language Web site. Mr. Romney quipped, “I love legal immigrants coming to the country, and I hope they vote for me.”

Sniping back and forth over immigration — particularly by Rep. Tom Tancredo of Colorado, a Buchananite — took up a significant portion of the debate. Republican voters will favor whichever candidate expressed their personal immigration position. Overall, however, the amount of Republican infighting over immigration strengthens an already strong hand for Democrats going into a potential general election. In past election cycles, it has been the Democrats who have faced divisive internal battles.

Still, a debate on a stormy night in June is a long way away from the New Hampshire primary and even longer, 17 months away, from the general election.