Fred Thompson entered yesterday afternoon’s Republican debate in Dearborn, Mich., as a national celebrity — but he left it as a regional candidate.

Mr. Thompson floated through the event, offering quips about being a member of the Screen Actors Guild and trading folksy comments about two characters on the “Andy Griffith Show” — Goober and Gomer. He also delivered flashes of President Reagan’s optimism, bits of fiscal conservatism, and chunks of sound foreign policy.

But while his first debate appearance was by no means a disaster, two candidates — Mayor Giuliani and Mitt Romney, who criticized each other and the Democratic front-runner, Senator Clinton — outshone him in equal measure. In addition, Senator McCain demonstrated that he remains a gritty, unbending presence in the race, not yet willing to give up.

If Mr. Thompson evoked Reagan when he described America’s economic prospects as “rosy,” Mr. Giuliani seemed to bring the Gipper to life when he proclaimed the soundness of New York City’s economic future, vowing that London would never overtake the Big Apple as the world’s financial capital. “Of course, London’s not going to replace New York. … Is the U.K. going to replace the United States of America?” he asked. “This is the strongest economy on Earth. It’s the last best hope of humanity.”

Mr. Romney also called on Reagan’s image by name, saying he would support a candidate in “the same mold as Ronald Reagan. And that’s somebody who is strong for our military, strong for our economy, and strong for our family values.”

The former Massachusetts governor also scored early in the debate by bringing up the tax increase supported by Governor Granholm of Michigan, an issue of intense interest to Republicans in the Great Lake State, where Mr. Romney’s father, George Romney, once served as governor.

Ms. Granholm, a Democrat, “has made a big mistake by raising taxes,” Mr. Romney said. “I was, frankly, a little nervous to be here tonight. I figured she was going to put a tax on the debate before we got finished.”

Mr. McCain also mentioned Reagan on the issue of trade.

“And all of this stuff about free trade — my dear and beloved Ronald Reagan, with all this bashing of free trade, he must be spinning in his grave.”

Moments when Messrs. Giuliani and Romney verbally sparred with each other diminished Mr. Thompson by pushing him to the periphery of the discussion.

Mr. Giuliani took issue with Mr. Romney’s record on taxes in Massachusetts, which had the effect of elevating the former governor. “I controlled taxes. I brought taxes down by 17%. Under him, taxes went up 11% per capita. I led; he lagged.”

Mr. Romney countered by calling Mr. Giuliani’s assertions “baloney.”

As far as the substance of the exchange, the executive director of the Beacon Hill Institute — a Massachusetts, think tank that promotes fiscal conservativism — David Tuerck, told the Sun that Mr. Romney had raised fees and closed “loopholes” during his time as governor but deserved an

“A-” for holding the line on income tax increases in the face of a Democratic Legislature pushing for one.

A weak moment for Mr. Romney came when he was asked whether he would seek congressional approval before taking military action against Iran. Mr. Romney gave the answer of a corporate executive wanting to comply with Sarbanes-Oxley financial reporting requirements. “You sit down with your attorneys,” he said, which opened him up to attack from Ron Paul, who said, “this idea of going and talking to attorneys totally baffles me.”

Mr. Giuliani, by contrast, used Mr. Paul as a foil to remind Americans of the September 11, 2001, attacks. “And the point of … Mr. Paul … that we’ve never had an imminent attack, I don’t know where he was on September 11th,” Mr. Giuliani said. “And if we had known about it, maybe hitting a target [in Afghanistan] quickly might have helped prevent it.” He then segued into a critique of Mrs. Clinton for refusing to answer whether she would use military force to prevent Iran from acquiring nuclear weapons.

Mr. Thompson gave a respectable, common-sense answer on the danger posed by Saddam Hussein prior to America’s invasion of Iraq.

“There’s no question that if left to his own devices, he and his son would still be running that place, attacking their neighbors and murdering their own people, and developing a nuclear capability — especially in looking at what Iran is doing as their next-door neighbor and long-time adversary,” he said.

But he seemed too eager to burnish his credentials as a Southerner when a former governor of Arkansas, Mike Huckabee, made an allusion to Nascar and two characters from the 1960s television program “The Andy Griffith Show.”

In a discussion on ethanol, Mr. Thompson seemed to be attempting to “out-South” Mr. Huckabee.

“We can’t wait until another generation,” Mr. Huckabee said, stressing the urgency of developing alternatives to Middle East oil. “Instead of running it like Nascar, we’ve been running it like taking the family station wagon in for letting Goober and Gomer take a look at it when they get time, under the shade tree.” Mr. Thompson responded: “I want to explain for my friends here who Goober and Gomer are.”

It’s possible that Mr. Thompson’s subdued performance was a calculated effort to appeal to voters in South Carolina and shore up his support in the South. Yet by not dominating the stage, his nascent campaign lost ground to more assertive opponents.