In his first debate, Fred Thompson looked like a football player who missed the first month of practice. So he stretched his muscles and ran laps, while his teammates scrimmaged and perfected their game plans.

As Rudy Giuliani and Mitt Romney challenged each other on taxes and spending and took shots at Democratic front-runner Hillary Rodham Clinton, Thompson concentrated on presenting his own views, somewhat uncertainly at first, then with more confidence. But he failed to delineate a clear persona, speaking mainly in generalities and ignoring his rivals.

By the end of the two hours Tuesday, the former Tennessee senator had done nothing to bolster or damage his candidacy, leaving his place in the complicated Republican presidential field no more clearly defined than it had been before he joined it.

While his camp seemed satisfied and his poll numbers have been good, Thompson still faces a basic challenge of establishing his role in the race, lest the opening tests in Iowa, New Hampshire and Michigan define it as a Romney-Giuliani contest before South Carolina, the first test in Thompson’s native South.

The only time he challenged anyone on stage came when moderator Chris Matthews said he should have cut off a lengthy answer on the government’s role in auto company/union talks. “That’s your opinion, Chris,” Thompson snapped, an exchange that might win plaudits from the many GOP critics of the media.

His best “sound bite” moment came in response to a sarcastic rejoinder from Romney.

“This is a lot like ‘Law & Order,’ senator,” Romney said, referring to the long-running television series Thompson joined after leaving the Senate. “It has a huge cast, the series seems to go on forever, and Fred Thompson shows up at the end.”

“And to think I thought I was going to be the best actor on the stage,” replied Thompson, a veteran of movies as well as TV.

Most of Thompson’s policy answers were far less succinct.

Typical was one on the dangers of a weak dollar. “It will damage us internationally,” he said. “We’ve got to have a strong dollar because of the creditors that we have there. It helps our exports to a certain extent now, and we’re enjoying that part of it.”

Similarly, when asked at the outset how to ensure economic vibrancy, he recited a series of upbeat economic statistics that started “with the tax cuts that we put in place” but warned that “we are on a mandatory spending lockdown that is pushing us in a direction that is unsustainable.”

On Iraq, he said: “I think the policy that we’re engaged in now is the right one. Clearly, to me, we didn’t go in with enough troops, and we didn’t know what to expect when we got there. But now we’re showing signs of progress. I think we got to take advantage of the opportunities that we have there, now that we see a window of opportunity for things to turn around and us to stabilize that place and not to have to leave with our tail between our legs.”

His rivals were more specific on Iraq.

Sen. John McCain noted that he was the only one on stage who said four years ago, “This is failed policy on Iraq.” Sen. Sam Brownback said the political aspect has been “poorly done,” citing the bipartisan plan he and Democratic hopeful Joseph Biden are pushing for a three-state solution.

Thompson was strictly a bystander as Giuliani and Romney provided some fireworks when asked about their economic differences.

“I brought taxes down by 17 percent,” Giuliani said. “Under him (Romney), taxes went up 11 percent per capita. I led; he lagged.”

Romney shot back, “It’s a nice line, but it’s baloney, Mayor. You’ve got to check your facts. I did not increase taxes in Massachusetts; I lowered taxes.” And he noted that the Club for Growth, a conservative organization, said his spending grew 2.2 percent, compared with Giuliani’s 2.8 percent.

Romney also challenged Giuliani’s action in fighting a Clinton administration law to give the president the line-item veto, letting him reject specific spending items.

“I don’t think it’s a bad idea to have a Republican presidential candidate who actually has beat President Clinton at something,” Giuliani said.

Thompson summed up by saying, “I’ve got to admit it was getting a little boring without me, but I’m glad to be here now.” He’ll need more than mere presence to generate excitement in future debates.