WEST HARTFORD, Conn.— Senator Lieberman, facing his first primary challenge in his 18-year Senate career, sought to distance himself from the Bush administration yesterday night in the only scheduled debate with Democratic primary challenger Ned Lamont.

The debate, on WVIT-TV, paired off Connecticut’s junior senator with a stronger than expected challenger who has made Mr. Lieberman’s support for the Iraq war the centerpiece of his campaign.

Mr. Lieberman, 64, who is running for a fourth-term, is facing an August 8 primary battle. Just six years after being his party’s nominee for the vice presidency, Mr. Lieberman has fallen into disfavor among some Democrats for his perceived closeness to President Bush.

“Ned Lamont seems just to be running against me based on my stand on one issue, Iraq, and he is distorting who I am and what I’ve done,” Mr. Lieberman said in his opening statement.

“I know George Bush. I’ve worked against George Bush. I’ve even run against George Bush. But Ned, I’m not George Bush,” Mr. Lieberman said. “So why don’t you stop running against him and have the courage and honesty to run against me and the facts of my record.”

Mr. Lieberman said he has opposed Bush on most of the major policy initiatives of his administration, from tax cuts for the rich to privatizing Social Security.

Mr. Lamont, 52, a former Greenwich selectman and newcomer to state politics, has gained in statewide polls by accusing Mr. Lieberman of straying from his Democratic roots. Founder of a cable television company, Mr. Lamont has dumped more than $1.5 million of his own money into the race. Mr. Lamont said yesterday that he’s prepared to invest more, possibly $1 million.

Mr. Lamont said during the debate that he was not a traditional politician and he touted his community service, from serving as a selectman in Greenwich to volunteering as a teacher.

“In Washington, we’re making a lot of bad choices right now,” Mr. Lamont said in his opening statement. “We’re losing a lot of our good paying jobs here in the state of Connecticut, and I wonder about the opportunities for our kids as they get older.

“And Senator Lieberman, if you won’t challenge President Bush and his failed agenda, I will,” he said.

Mr. Lamont cited rising gas prices and health care costs. And he repeated his opposition to the war in Iraq.

“We have 135,000 of our bravest troops stuck in the middle of a bloody civil war,” he said. “And I say … those who got us into this mess should be held accountable. Let’s have the debate.”

The race has garnered national attention and was also televised by MSNBC and C-SPAN.

Interest intensified Monday when Mr. Lieberman announced he would begin collecting signatures to petition his way onto the November ballot as an independent candidate should he lose the primary. As of yesterday, Mr. Lieberman’s campaign had not yet sought petitions from the secretary of the state’s office.

Mr. Lieberman said during the debate that he has worked with Republicans, and he said those efforts have helped save the Naval submarine base in Groton from closure, clean up Long Island Sound and bring more transportation funding to Connecticut.

Mr. Lamont accused Mr. Lieberman of undermining Democrats on issues such as protecting Social Security, strengthening affirmative action laws and fighting school vouchers.

Mr. Lieberman also said Mr. Lamont’s views on issues, including free trade, have been inconsistent. He said Mr. Lamont voted with Republicans while on the Greenwich Board of Selectmen. He also noted that Mr. Lamont has contributed to his campaign.

“What changed is some people convinced him that he has a chance to become a U.S. senator,” Mr. Lieberman said.

Mr. Lamont said he was going to fight for change in Washington, and he was going to be a “change agent.”

Both candidates did agree on one issue, that illegal immigrants should be provided a pass to earn legal status.

Scott McLean, chairman of the political science department at Quinnipiac University, said before the debate that Messrs. Lamont and Lieberman had different things to prove.

“Lieberman needs to manage to convince people that he’s still a Democrat,” Mr. McLean said. “And I think Lamont, he has to do the opposite of course. I think he has to show people why he would be a better person in the Senate, and that’s the hardest job.”

Mr. Lamont, he said, not only has to attack Mr. Lieberman’s party loyalty but give voters a reason to vote for him as well.

“It’s going to be a harder job for Ned Lamont, but he’s got a huge opportunity here,” Mr. McLean said. “People are paying attention. People want to see what happens. It’s sort of like watching a car wreck.”

The Quinnipiac University Poll has shown Mr. Lamont’s support among registered Democrats increasing from 19% in May to 32% in June. Mr. Lieberman’s support in the same period fell from 65% to 57%.

But the same poll predicted Mr. Lieberman winning with 56% of the vote if he runs as an unaffiliated candidate, compared with 18% for Mr. Lamont and 8% for Republican Alan Schlesinger.