Fred Thompson — veteran actor, former Republican senator — launched his bid for the presidency Hollywood style.

"I'm running for president of the United States," Thompson told Jay Leno in a taped appearance on NBC's "Tonight Show" airing Wednesday night. "It starts right now."

Thompson called top opponents Rudy Giuliani, Mitt Romney and John McCain formidable but added: "I think I will be, too" as he rejected the notion that he was getting into the race too late, only four months before voting begins.

"I don't think people are going to say, 'You know, that guy would make a very good president but he just didn't get in soon enough,"' Thompson said as the studio audience laughed. Poking at his rivals who have been running since the year began, he added: "If you can't get your message out in a few months, you're probably not ever going to get it out."

In a multi-phased campaign rollout, Thompson also called attention to his candidacy with a 30-second ad broadcast during a Republican debate in New Hampshire that he skipped. He will explain the rationale for his candidacy during a 15-minute Webcast on his campaign Internet site just after midnight.

Thompson, 65, enters a crowded GOP field and an extraordinarily fluid race four months before the first votes are cast. While Giuliani leads in national polls, Romney maintains an edge in the early voting states of Iowa and New Hampshire. Overall, Republican voters have expressed less satisfaction with their choices than Democrats, and Thompson sees that as an opening for his candidacy.

It won't be easy for the former Tennessee senator. His campaign has been beset by lackluster fundraising and multiple staff changes, the most recent coming Tuesday with the departure of his spokesman of just two weeks, Jim Mills.

His made-for-television entry — and absence from the debate — didn't go over well with some people gathered to see the candidates at the University of New Hampshire in Durham. Several of Thompson's rivals took turns jabbing at him and warning that the nomination must be earned through hard work and shoe-leather politicking.

"Fred is from Nashville, Tennessee, home of George Jones, who was often called no-show George for not showing up at his concerts. And maybe Senator Thompson will be known as the no-show for the presidential debates," chided former Arkansas Gov. Mike Huckabee. Joked McCain: "Maybe we're up past his bed time."

"The only question I have for Senator Thompson is: Why the hurry? Why not take some more time off? Maybe January, February might be a better time to make a final decision about getting in this race," Romney quipped. On a serious note, Giuliani said: "This is not a time that the United States should be electing someone who's gonna get on-the-job training. You need people with executive experience."

As people waited in line to see the debate, one person ran around in a yellow duck suit carrying a sign that asked, "Fred, why are you ducking the debate?"

"He should be here," said Bob Crossley, 50, a real estate agent from Wolfeboro, N.H. "It's kind of like defaulting in sports. If you don't show up, you lose."

Thompson told Leno: "We'll have an opportunity to debate a lot ... We'll do our fair share."

He starts some eight months after his eight rivals began campaigning, and he lags behind Giuliani and Romney in both money and organization. In June, Thompson fell short of his $5 million fundraising goal by $1.5 million.

Still, Thompson consistently ranks among the top Republicans in national polls and state surveys. A Southerner with a mostly right-leaning Senate record and a plainspoken style, he is looking to capitalize on discontent with the current choices among conservatives who make up a significant segment of GOP primary voters.

They have not yet settled on a candidate and are searching for someone with like-minded credentials who can win in a general election.

Thompson is perhaps best known to millions of Americans as the gruff district attorney Arthur Branch on NBC's crime drama "Law & Order," as well as for his roles in more than a dozen movies.

During his 1994-2002 Senate tenure, he was considered a reliably conservative vote. He strayed from the party line on a few issues, including advocating for campaign finance reform. He also was McCain's campaign co-chairman in 2000 instead of backing establishment candidate George W. Bush.

Thompson spent many years in Washington as a lawyer and lobbyist. He has faced repeated questions about his lobbying work for a family planning group that sought to relax an abortion rule and former leftist Haitian leader Jean Bertrand-Aristide.

Late-night talk shows have become a popular place for politicians to announce they are candidates for public office. Earlier this year, McCain announced his presidential bid on CBS' "Late Show With David Letterman." Arnold Schwarzenegger disclosed to Leno his plans to run for California governor.