Rep. Lynn Woolsey made it official Monday at her Petaluma home, announcing that she will retire next year after completing two decades as the North Bay's representative in Congress.

"It's been a privilege to serve you, to work with you, and I thank you from the bottom of my heart," Woolsey, 73, told about 200 supporters gathered in the backyard of her Petaluma home.

When her current term, her 10th, expires at the end of 2012, "It will be time for me to move on," she said.

Woolsey identified several accomplishments in her district, including twice saving the Two Rock Coast Guard base from closure, establishing a school breakfast pilot program that included Santa Rosa and getting the former Skaggs Island naval facility converted to a national wildlife refuge.

The Democrat and former Petaluma city councilwoman was elected to Congress in 1992, the "year of the woman" in American politics. A former welfare mother who founded her own personnel agency in Petaluma, she became known for her early opposition to the Iraq war and continued opposition to the conflict in Afghanistan.

"Nothing has animated me more than opposition to the wars our country has been fighting for the last 10 years," she said, calling them a "moral blight on this nation."

Last week she faulted President Obama's Afghanistan troop withdrawal plan as too small and too slow, calling it "a profound disappointment."

Rep. Barbara Lee, D-Oakland, introduced Woolsey — whom she referred to as "my girlfriend" — to the crowd.

"You know she is a warrior for peace and justice," said Lee, who co-chaired the Congressional Progressive Caucus with Woolsey.

Woolsey, who has four grown children and five grandchildren, said that family figured in her decision to retire.

"I want to be home more," she told reporters. "I want to get off those airplanes."

But Woolsey, saying she is "100 percent" healthy, will continue to be active as a member of Americans for Democratic Action, an independent liberal lobbying organization founded by Eleanor Roosevelt, economist John Kenneth Galbraith and others.

"It will be hard to slow down," said Woolsey, who is president of the organization. "I've got more energy than the average bear."

In terms of unfinished business, Woolsey said she would most like to see passage of her bill expanding two marine sanctuaries, adding the coast from Bodega Head north to Point Arena to an area off-limits to offshore oil development.

Conservatives in her district, which covers Marin and most of Sonoma County, have chafed at Woolsey's liberal politics. But in a district in which Democrats hold a more than 2-to-1 voter registration advantage over Republicans, Woolsey easily rolled to re-election nine times.

Challenged last year by Republican Jim Judd, a Rohnert Park businessman, Woolsey won her 10th term with 66 percent of the vote. The job currently pays $174,000 a year.

A few weeks before the 2010 election, Woolsey said she had no plans to retire. "I've got the health, the energy and the desire," she said at the time.

But in December, Woolsey said she was considering retirement, noting that she will be 75 and will have served 20 years on the Hill by the end of her current term. Woolsey said then that she would make her decision in June.

Assemblyman Jared Huffman, D-San Rafael, and Marin activist Norman Solomon subsequently announced plans to run for the seat if Woolsey retired. Both have raised more than $100,000 for a campaign they acknowledged could cost more than $1 million.

Susan Adams, a Marin County supervisor, also has formed a campaign committee and said she is "exploring the opportunity." Adams said Monday she would make a decision "pretty shortly." All three potential candidates attended Woolsey's announcement, along with numerous local politicians.

Woolsey said she will make no endorsement in the upcoming race to fill her seat.

Petaluma Mayor David Glass said Woolsey "has been a leader on so much for this district," including the Petaluma River flood control project.

"I was hoping she would say she is going to stay another two years," Glass said.

Lynn Hamilton, a former Sebastopol mayor, said Woolsey stuck to her principles and supported "just about every progressive issue you could think of."

"I am just so proud of her," Hamilton said. "I just love her."