With the Democratic primary taking place tomorrow in Connecticut, Senator Lieberman is going on the offensive and in the fight for his political life as his opponent, Ned Lamont, rides the momentum of an anti-war message.

After months of fending off criticism about his support of the Iraq war and his coziness with President Bush, Mr. Lieberman delivered a speech last night that attempted to convince voters that his independent style is an asset in Washington.

“That’s something that separates me from my opponent — I don’t hate Republicans,” Mr. Lieberman said at a community center in East Haven, Conn. “I know that sometimes the best way to get things done in the Senate for my constituents is through bipartisan cooperation.That doesn’t make me a bad Democrat. It makes me a better senator.”

Mr. Lieberman — who has been in the Senate 18 years and had enough popularity among Democrats just six years ago to be named the vice presidential nominee — has for the past few months found himself in the unfamiliar role of the underdog.

His election is being closely watched by Democrats around the country and will serve as a cue for whether voters in the party are going to welcome more moderate, independent-minded candidates, like Mr. Lieberman, or if they are going to move further to the left.

Mr. Lamont has spent about $4 million of his fortune to fund the campaign and air a slew of advertisements.

“They have taken their toll,” the senator’s campaign manager, Sean Smith, said yesterday, referring to Mr. Lamont’s commercials.

Mr. Smith said the campaign will “combat” Mr. Lamont’s advertising with a final round of television ads. To do that, Mr. Smith said, the campaign would reduce part of its Election Day field operation. The decision is risky, but the Lieberman camp is hoping it will pay dividends at the voting booth.

“They made as much as they could of his relationship with Bush,” political consultant Joseph Mercurio said.

So far, Mr. Lieberman’s message of being a “good Democrat” who has “been there” for Connecticut residents has not slowed his opponent’s meteoric rise in public opinion polls. Even an appearance by President Clinton has done little to lift Mr. Lieberman out his underdog status.

A June 8 Quinnipiac University poll found that the three-term senator led Mr. Lamont, a businessman, 55 to 40. By July 20, Mr. Lamont had a lead of four percentage points — double the margin of error. Last week’s poll, conducted after President Clinton campaigned with Mr. Lieberman, showed Mr. Lamont leading 54% to 41%.

More critical ads from Mr. Lieberman also have done little to slow Mr. Lamont. In one ad, Mr. Lamont is depicted as a bumbling cartoon cub taking orders from an older bear, representing the Republican senator Mr. Lieberman ousted in 1988 to win the seat, Lowell Weicker Jr. When the bear tells the cub to run against Mr. Lieberman “as a Democrat,” the cub protests, saying, “But I agree with Republicans 80% of the time.” The line referred to Mr. Lamont’s voting record when he was a member of the board of selectmen in Greenwich, Conn.

The message backfired.

That line is now featured on Mr. Lamont’s Web site, as a ringtone his supporters can download.

Other ringtones on the site feature Mr. Lieberman praising the Federal Emergency Management Agency, which was criticized for its handling of Hurricane Katrina in New Orleans. “FEMA of course has done an outstanding job,” Mr. Lieberman is heard saying.

On another ringtone, Mr. Lieberman says he supports reappointing FEMA’s director, Michael Brown, who oversaw the Katrina response.

Mr. Lamont’s radio ads are more blunt in the critique of Mr. Lieberman.

In one radio ad, an elderly sounding woman tells listeners in a stern voice, “If our leaders aren’t getting the job done, get ’em out!”

In another ad, Mr. Lamont starts by describing himself as “a guy who started up his business from scratch,” referring to his multimillion-dollar cable company, Lamont Digital Systems.

Halfway through the one-minute ad, Mr. Lamont says, “If Joe Lieberman is not willing to challenge President Bush and Vice President Cheney, then I will.” He goes on to say, “And if Joe Lieberman won’t stand up for 132,000 brave American troops stuck in the middle of a bloody civil war, I will.”

Bloggers unhappy with Mr. Lieberman’s support for the president and the war in Iraq have help spread Mr. Lamont’s message. National Web sites like MyDD and the online activist group MoveOn.org have embraced Mr. Lamont largely due to his opposition to the war.

New York Internet activist also have embraced Mr. Lamont’s cause. Opportunities to volunteer for him have been posted on the Web site Democracy for NYC, which spun out of the Internet volunteer effort from Governor Dean’s presidential campaign.

Another liberal Web site contributor, Michael Boulding of the Daily Gotham, joked that while in Connecticut for a wedding, “I hope to do some clandestine pro-Lamont proselytizing.” That may not be hard to imagine for liberal activists. Last week, the site published an e-mail seeking volunteers for Mr. Lieberman, reportedly sent from Princeton University’s Republican club.

Mr. Lieberman has said that if he loses tomorrow’s primary, he will run in the general election as an independent. Senator Clinton and others have said they will support whomever wins the Democratic primary.