Setting the stage for what could be a historic gubernatorial recall election, a group trying to oust Wisconsin Gov. Scott Walker says it has collected nearly enough signatures to force a vote on the Republican leader.

United Wisconsin said Thursday it has gathered signatures from 507,533 Wisconsinites, about 33,000 fewer than needed. The group wants to have 720,277 signatures by the Jan. 17 deadline to ensure it has enough valid names.

"The response has been really breathtaking and is a testament to the anger people have about what Walker has done to our state," said Meagan Mahaffey, the group's executive director.

More than 25,000 volunteers are fanning out, from the St. Croix River Valley to Beloit, to gather the remaining signatures, collecting names at a rate of about 18,000 a day, organizers say.

Walker has said he expects opponents to gather the needed signatures. That means the first-term governor, who has garnered a national reputation as a budget cutter not afraid to take on powerful unions, is likely to face the political fight of his life.

"Governor Walker is focused on the opportunity to once again take his message to Wisconsin voters," said Ciara Matthews, spokeswoman for Friends of Scott Walker. "He has worked tirelessly during his first year in office to lay the foundation for a more successful Wisconsin and to put state government back on the side of taxpayers."

Democrats support the recall effort despite not having a candidate yet to face Walker. The biggest name, former U.S. Sen. Russ Feingold, has taken himself out of the running. State Sen. Tim Cullen of Janesville has said he will run. Possible candidates include the man Walker beat last year, Milwaukee Mayor Tom Barrett, and former U.S. Rep. Dave Obey of Wausau.

Political firestorm

Walker ignited a political firestorm last winter that turned Madison, the state capital, into ground zero in the national fight between public employees and conservatives determined to wrestle down state government spending. To resolve a state budget deficit, Walker proposed limiting collective bargaining rights for public workers and sought sharp increases in their contributions to health care and pension costs.

Mahaffey said Walker pushed his conservative values further than he ever hinted during the 2010 campaign, which she said is why the petition effort has been so strong.

"This is not just a Madison or Milwaukee thing," she said.

It's unclear when a recall election would take place.

Signatures must be verified, and a primary would push the election further out.

Charles Franklin, political science professor at the University of Wisconsin-Madison, said the election would likely be between mid-April and late May.

Walker and allies fight back

Walker's campaign and the head of the Wisconsin Republican Party sued the state elections board on Thursday, saying its process for reviewing signatures on recall petitions is unconstitutional.

The lawsuit asks a judge to order the Government Accountability Board to look for and eliminate duplicative signatures, obviously fake names such as Mickey Mouse and obviously illegible signatures. The board has said state law places the burden of challenging those signatures on the officeholder targeted for recall.

Only two U.S. governors have been recalled: Gray Davis in California in 2003 and Lynn Frazier in North Dakota in 1921.

Democrats also are circulating petitions targeting four GOP state senators. Two Republicans were ousted in recall votes over the summer, leaving the GOP with a 17-16 majority in the Senate.

Aside from the uproar in Madison, Walker has been wounded by sluggish economic growth, Franklin said. Walker's chief campaign pledge was to rejuvenate the state's ailing economy. After steady job growth in the first half of 2011, growth has been small or nonexistent in the public and private sectors, Franklin said.

Stephan Thompson, head of the Wisconsin Republican Party, said Walker will have a "great chance" in a recall election. He described Walker's possible opponents as "a list of tired, old, defeated liberal candidates.''

Wisconsinites will take a look at the field, Thompson said, and decide "we do not want to go back to the failed policies of the past.''

The Associated Press contributed to this report. • 651-222-1288 • 651-925-5042