STAMFORD — Flanked by family and supporters, U.S. Sen. Joseph Lieberman ’64 LAW ’67 announced Wednesday that he will not run for a fifth term in 2012, ending a career as an elected official that has spanned nearly four decades.

Returning to his hometown of Stamford to deliver a prepared speech, Lieberman acknowledged that a re-election bid would have been difficult, and said it was time for him to “turn the page.”

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“The reason I have decided not to run for re-election in 2012 is best expressed in the wise words from Ecclesiastes: ‘To everything there is a season, and a time to every purpose under Heaven,’” said Lieberman, an Orthodox Jew. “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.”

But this may not be the end of politics for Lieberman, an embattled Democrat who became an Independent in 2006 after losing the Democratic primary to Ned Lamont SOM ’80; in his speech, he pledged he will stay politically active, just outside of elected office.

“I will keep doing everything in my power to build strong bridges across party lines — to keep our country safe, to win the wars we are in, and to make sure America’s leadership on the world stage is principled and strong … I look forward to new opportunities that will allow me to continue to serve our country, and to stay engaged and involved in the causes that I have spent my career working on, and that I care so much about,” Lieberman said.

For Lieberman, the Stamford Marriott Hotel and Spa where he made the announcement holds a special significance — his first home, he said, once stood on the land the hotel now occupies.

Across the nation, Democrats and Republicans alike celebrated Lieberman’s lengthy career, despite past clashes. Republican Sen. Susan Collins of Maine, the ranking Republican on the Homeland Security Committee that Lieberman chairs, called him a “trusted colleague” and “good friend” in a statement Wednesday.

“He is a man of conscience … We are all the better for his service in the U.S. Senate, and I will deeply miss him,” Collins said. She also celebrated his leadership on last month’s repeal of “Don’t Ask, Don’t Tell,” the Clinton-era policy that prevented gays and lesbians from serving openly in the military, as one of Lieberman’s major accomplishments.

Many of Lieberman’s most celebrated achievements center around defense issues; in a Wednesday statement, Homeland Security Secretary Janet Napolitano credited him with the very creation of the Department of Homeland Security, and for his efforts to keep America safe.

“Dating back to the first days after 9/11, he has been an instrumental architect of the very way we work to keep America safe from the evolving threats we face in the 21st century,” Napolitano said.

Where Lieberman is headed remains unclear, but it may not be back to his Westville home; Republican Sen. John McCain, whom Lieberman controversially endorsed over President Barack Obama in the 2008 presidential race, suggested in an interview with CNN that Lieberman could be the next Secretary of Defense once Robert Gates retires.

With Lieberman out of the fray, the race to become Connecticut’s newest senator is wide open; Secretary of the State Susan Bysiewicz ’83, a Democrat, jumped into the race Tuesday, but so far she is the only candidate to officially declare. U.S. Rep. Chris Murphy of Cheshire and Rep. Joe Courtney of Vernon, both Democrats, have expressed interest in the race.

On the Republican side, Linda McMahon, the World Wrestling Entertainment executive who lost to Democratic Sen. Richard Blumenthal LAW ’73 last fall in race for the seat vacated by Democrat Chris Dodd, and Tom Foley, a businessman and former ambassador to Ireland who lost to Gov. Dannell Malloy in November, have both said they would not rule out another run.