HARTFORD, CONN. — Democratic challenger Ned Lamont, riding strong opposition to the war in Iraq, has surged into the lead over Senator Lieberman, a Democrat of Connecticut, in Tuesday’s Senate primary, according to a newly released Quinnipiac University poll.

Mr. Lamont leads Mr. Lieberman 54% to 41% in the poll and now has clear momentum over the three-term incumbent and former Democratic vice presidential nominee. The findings represent a setback for Mr. Lieberman, who claimed earlier this week that a July 24 visit by President Clinton had turned around his campaign.

Mr. Lieberman has been sliding throughout the summer as Mr. Lamont’s candidacy has picked up energy and support. In June, the Quinnipiac poll showed Mr. Lieberman leading 55% to 40%. Shortly before Mr. Clinton’s visit, the poll found Mr. Lamont edging ahead 51% to 47%.

Mr. Lieberman has only a handful of days to reverse the trends if he hopes to salvage the Democratic nomination. He has said he plans to run as an independent if he loses to Mr. Lamont on Tuesday, but a landslide rejection by members of his own party could complicate his hopes of running a successful third-party candidacy.

The two candidates appeared briefly together on Wednesday at a rally denouncing the giant retailer Wal-Mart, but otherwise, they have been on separate and significantly different tracks this week.

Mr. Lieberman has been rolling through the state on his green campaign bus, dubbed “Joe’s Tomorrow Tour,” stopping at senior citizen centers, diners, restaurants, markets, construction sites, and retail outlets. But he has been met by small crowds and minimal enthusiasm, save for some of his old friends in organized labor and among local elected officials.

Mr. Lamont comes to his events in a hybrid SUV and has won repeated applause from his supporters whenever he attacks Mr. Lieberman for supporting the Iraq war and for failing to stand up to President Bush.

On Wednesday, Mr. Lamont campaigned in African-American churches in Bridgeport and New Haven with Jesse Jackson and Al Sharpton. The two black ministers and politicians urged Connecticut voters to send a message to Mr. Bush and the nation on Tuesday.

The Quinnipiac poll painted a gloomy picture for Mr. Lieberman’s campaign team. Mr. Lamont led among virtually every category of voter, except those with incomes below $30,000, where Mr. Lieberman led 49% to 46%.

Mr. Lamont held a commanding lead among college-educated Democrats (57% to 39%) but also leads among those without a college degree (51% to 43%). Mr. Lieberman had hoped to rally support among blue-collar and working-class Democrats, but the poll suggests Mr. Lamont also has broken through among those voters.

Among self-identified liberals, Mr. Lamont leads 66% to 31%. Mr. Lieberman holds a narrow edge among self-identified moderates, with 49% to 45%.

Mr. Lamont has built his advantage almost entirely on dissatisfaction with Mr. Lieberman, according to the poll. Among his supporters, 65% said their vote was more against Mr. Lieberman than for Mr. Lamont. The poll showed that the once-popular Mr. Lieberman has lost considerable appeal to his party’s rank and file. Just 37% of those surveyed said they had a favorable impression of Mr. Lieberman, while 34% said they viewed him unfavorably. Ironically, those findings were marginally better for Mr. Lieberman than Quinnipiac’s previous poll.

Mr. Lamont is viewed favorably by 46% of those surveyed, compared with 14% who view him unfavorably. That represents a 10-point jump in favorability since a July 20 poll.