Updated

As Democratic Sen. Joe Lieberman fights for his political life, his campaign on Tuesday accused his opponent's backers of hacking into the senator's campaign Web site and shutting it down just in time for Connecticut's primary Election Day.

The site, www.joe2006.com, has been shut down since about 7 p.m. ET Monday. Campaign officials say they are asking for an investigation by federal and state authorities, not only because hacking is a cybercrime, but because shutting down the site ahead of Tuesday's vote denies supporters the opportunity to read about their candidate or look for polling stations that were available on the site.

"The campaign has notified the U.S. Attorney and the Connecticut Chief State's Attorney, and the campaign will be filing a formal complaint reflecting our concerns. The campaign has also notified the State Attorney General Dick Blumenthal for his review," a statement reads.

The campaign's Webmaster issued a statement saying the denial of service is not a result of any overdue bills or other actions on the part of the campaign. Campaign manager Sean Smith called the electronic infiltration a "dirty trick" and said primary opponent Ned Lamont should denounce the action.

"We've double- and triple-checked every internal possibility that this could have been. We're confident that this was done from the outside," Smith told FOX News. "That's why we've asked for our opponent Ned Lamont to denounce this kind of politics. It's a deliberate attempt to suppress the vote here in Connecticut. It's wrong and he should stand up and say so and demand whoever was behind this to stop immediately."

Lieberman was campaigning around the state for last-minute votes in a race that until Monday had seemed a lock for Lamont, a millionaire owner of a cable news company who has won support for his calls to have U.S. troops pull out of Iraq. A Quinnipiac University poll released Monday showed that Lieberman had cut Lamont's lead from 13 points to 6 points in the week leading up to Election Day.

Campaigning Tuesday in New Haven, Lieberman said he has no proof that Lamont supporters are responsible, but was asking the state party chairman to intervene.

"I'm concerned that our Web site is knocked out on the day of the primary, you'd assume it wasn't any casual observer," Lieberman said.

Lamont, campaigning in the early afternoon in Bridgeport, called the accusation "just another scurrilous charge." His campaign denied involvement and said the primary day accusation is a sign of Lieberman's desperation.

A spokesman for the U.S. Attorney's office declined immediate comment. Calls placed to the FBI and the chief state's attorney's office seeking comment were not immediately returned.

Smith said the site began having problems Monday night and crashed for good at 7 a.m. The problem also affects all the campaign's e-mail accounts.

"We have no ability to communicate with our supporters and our people who are out working for us," Smith said. "We have no ability for voters to contact our campaign through e-mail. ... It's Election Day, Joe Lieberman is surging back into victory, every poll indicated. People who want to stop that have sabotaged this campaign."

If defeated, Lieberman would be only the fourth incumbent senator since 1980 to lose a primary election. Quinnipiac Poll Director Douglas Schwartz said the latest poll shows people may be having second thoughts about Lamont, whose only political experience is two years as a Greenwich selectman and six years on the town's Board of Estimate and Taxation.

The three-term senator, nationally known for his centrist views, has endured harsh criticism in his home state for supporting the Iraq war and has been labeled by some Democrats as too close to Republicans and President Bush, a charge Lieberman says distorts his record.

The race has attracted tremendous interest, both in Connecticut and nationally. More than 14,000 Connecticut voters switched their registration from unaffiliated to Democrat to vote in the primary, while another 14,000 new voters registered as Democrats, according to state statistics.

Secretary of the State Susan Bysiewicz said she expected turnout of 40 percent, much higher than the 25 percent turnout that is typical of state primaries. She said poll workers were expecting the heaviest turnout in the late afternoon, as people went home from work.

"I'm completely for Lamont because of the war issue," said William Clement, 57, who voted in Hartford's west end Tuesday morning. "I'm totally disgusted with Lieberman and his positions. I think he sold us out."

Norwich's Raymond Deauchemn, 55, said he voted for Lamont. "I don't think Lieberman is doing that great of a job. He's more like Bush than anything else. I think he's his little puppet."

Hartford resident Jack Ellovich of Hartford cast his vote Tuesday morning for Lieberman, although he said his wife voted for Lamont.

"He's got the experience, he's got the clout," said Ellovich of Lieberman. "He's already got the standing in the Senate. I think he can get stuff done for Connecticut and I don't think Lamont really knows how the system works."

Lieberman has said that if he fails in this primary, he will run for his seat as an independent. The back-up plan is similar to his 2000 vice presidential effort, in which he stayed on the state ballot as a Senate candidate just in case he and Al Gore lost.

Should Lieberman lose Tuesday, supporters would have until Wednesday afternoon to submit petitions to put Lieberman's name on the ballot as an independent, but depending on the size of his loss, he could come under pressure to abandon that plan. Several Democratic lawmakers and Lieberman backers have said they will support whoever the Democratic nomination is for the state.

Lamont, who was to campaign Tuesday in Greenwich, Bridgeport, New Haven and Hartford, told Hartford television station WTIC that he expected to win and send a message about the need to pull out of Iraq.

"I think we've got a good competitive race here," he said Monday, adding that recent polls are "little narrow samples" and that "everybody knows they bounce up and down."

Lieberman said he believes voters are coming back to him.

"I feel they were flirting with the other guy for a while, wanting to send me a message," he said Monday during a stop at a restaurant in Hartford. "I got their message. I think they want to send me back to Washington to continue working with them, fighting for them, and delivering for Connecticut."

Political observers have suggested that a Lieberman loss would hurt Democrats' national security credentials, but Lamont supporters say that a big win is an indication that many voices are allowed to participate in the party.

"It illustrates what the Democratic Party is all about, which is it's different from the Republican Party, which marches in lockstep," said Democratic strategist Michael Brown.

But Republican strategist Nancy Pfotenhauer said a Lamont win would demonstrate a "marriage of convenience among two components of the extreme left wing of the Democratic Party," namely billionaires and Hollywood types coordinating with the "netroots" or online bloggers and activists.

FOX News' Carl Cameron and The Associated Press contributed to this report.