While Lieberman’s supporters lamented his decision not to run in 2012, many constituents, especially Democrats, said they were pleased because the “Joe” they knew as a state lawmaker and activist state attorney general is already long-gone.

“I think Joe at one point was a really good legislator. … He was on the right side of the issues,” said Leslie Simoes of West Hartford, an advocate for people with disabilities and a registered Democrat. “And then, something shifted in him and he has just come out repeatedly, over and over and over again, absolutely on the wrong side of things.”

With his extended family standing behind him, Lieberman announced his intentions to retire before a crowd of several hundred supporters at a downtown Stamford hotel, near the site of his childhood home. While he acknowledged that he’d likely face a difficult re-election campaign, Lieberman, 68, downplayed speculation he was backing down from a tough race.

He invoked a Bible verse from Ecclesiastes in explaining his decision: “To everything there is a season, and a time to every purpose under Heaven.”

“At the end of this term, I will have served 24 years in the U.S. Senate and 40 years in elective office. For me, it is time for another season and another purpose under heaven,” he said.

Lieberman said he’s had a history of winning tough political battles since the 1970s, including the 2006 race where he lost the Democratic primary, only to win the general election as an independent.

“I know that some people have said that if I ran for re-election, it would be a difficult campaign for me. So what else is new,” Lieberman said.

Peter Zonis, a food industry consulant, lives in the same building in Stamford as Lieberman. He said he would like for his neighbor to run for another term, saying Lieberman has done a great deal for the state.

“I think he tried to be an independent voice. I think we need someone like him,” said Zonis. “I think we have too much partisanship.”

While Lieberman’s hawkish views on the military and the Iraq war rankled some Democrats, his support for gay rights and abortion rights won him the praise of many liberals.

Lieberman, whose poll ratings in his home state have slipped in recent years, nearly won the vice presidency on the Democratic ticket with running mate Al Gore in 2000 and mounted an unsuccessful presidential bid in 2004.

Gov. Dannel P. Malloy, the state’s new Democratic governor, called Lieberman a “steadfast and ardent advocate on behalf of the people of Connecticut.” Malloy, the former Stamford mayor, said he’s known Lieberman for years and that it is rare to come across someone like him who is not afraid to tell people where he stands, even if the stance is unpopular.

Lieberman has been at odds with the state Democrats since the 2008 presidential election. That’s when he appeared at the Republican National Convention, endorsed the GOP presidential candidate, Sen. John McCain, and publicly criticized Democratic President Barack Obama during the election. Some in the state party unsuccessfully attempted to have the party censure him.

While he didn’t specifically mention the state Democrats’ criticism, Lieberman acknowledged Wendesday he has “not always fit comfortably into conventional political boxes” and felt his first responsibility was to serve his constituents, state and country — not his political party.

Nancy DiNardo, the party’s chairwoman, credited Lieberman with dedicating a lifetime to public service.

“His 40-year body of work is replete with Democratic successes,” including his recent leadership of the repeal of the federal “don’t ask, don’t tell” ban on gays serving openly in the military.

The state’s Republican chairman, Chris Healy, said Lieberman’s “steadfast courage in defending the nation’s interests” won him many Republican supporters, noting the senator’s concerns about the threat Islamic fundamentalism posed to national security.

“These acts of courage and resolve almost cost Senator Lieberman his political career in 2006 when radical liberals ousted him as the candidate of the Democrat Party,” Healy said.

Hours before Lieberman’s plans became public on Tuesday, former Connecticut Secretary of the State Susan Bysiewicz said she would run in 2012 for Lieberman’s seat.

Reps. Chris Murphy and Joe Courtney are considering a run. Republican Linda McMahon is also seen as a potential challenger, despite losing her Senate bid last year against Democrat Richard Blumenthal. Former GOP Lt. Gov. Michael Fedele’s name has also been mentioned.

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Haigh reported from Hartford.