NEWTON, Mass. >> Democratic Rep. Barney Frank of Massachusetts announced his retirement Monday effective at the end of next year, closing out a congressional career of more than three decades capped by passage of legislation imposing new regulations on Wall Street.

Frank, 71 and a lifelong liberal, won a House seat in 1980 was one of the first lawmakers to announce that he is gay.

At a news conference, Frank said he had originally intended to seek one more term but changed his mind in part because the state’s new redistricting map will move 325,000 new constituents into his district.

He said he intends to remain active in public policy issues, including defending the so-called Dodd-Frank bill that he co-authored in the wake of the financial collapse of 2008.

"I think I will find my motives less impugned and I will be able to talk more about the merits," he said.

In a written statement, President Barack Obama paid tribute to Frank’s "passion and quick wit." He praised the Massachusetts lawmaker’s efforts to expand affordable housing, defend the rights of lesbian, gay, bisexual and transgender citizens and work to enact the "most sweeping financial reform in history."

Sixteen other Democrats have announced plans not to seek new House terms in 2012, compared with six Republicans.

As chairman of the House Financial Services Committee, Frank was instrumental in passage of the Dodd-Frank bill, which contained the stiffest restrictions on banks and Wall Street since the Great Depression. The measure clamped down on lending practices and expanded consumer protections to prevent a repeat of the 2008 meltdown that knocked the economy to its knees.

Some Republicans have vowed to seek its repeal, although they are unlikely to succeed.

Over the years, Frank consistently came down on the liberal side of public issues, opposing the war in Iraq and bills to cover its expenses.

At his news conference, he acknowledged one error, his vote against President George H.W. Bush’s request for support for a military campaign to force Iraqi leader Saddam Hussein’s withdrawal from oil-rich Kuwait.

The mission "worked well," Frank said in retrospect, saying he would have voted in favor had he known.

More than two decades ago, Frank was reprimanded by the House for using his congressional status on behalf of a male prostitute whom he had employed as a personal aide, including seeking dismissal of 33 parking tickets.

"I should have known better. I do now, but it’s a little too late," Frank said at the time.

Democrats rebuffed Republican calls for Frank’s expulsion, and instead, the Massachusetts Democrat resumed a career that far outlasted many of those who had sought his ouster.