General Motors filed for Chapter 11 bankruptcy protection Monday as part of the Obama administration's plan to shrink the automaker to a sustainable size and give a majority ownership stake to the federal government.

GM's bankruptcy filing is the fourth-largest in U.S. history and the largest for an industrial company. The company said it has $172.81 billion in debt and $82.29 billion in assets.

"The General Motors board of directors authorized the filing of a Chapter 11 case with regret that this path proved necessary despite the best efforts of so many," GM Chairman Kent Kresa said in a written statement. "Today marks a new beginning for General Motors. ... The board is confident that this New GM can operate successfully in the intensely competitive U.S. market and around the world."

As it reorganizes, the fallen icon of American industry will rely on $30 billion of additional financial assistance from the Treasury Department and $9.5 billion from Canada. That's on top of about $20 billion in taxpayer money GM already has received in the form of low-interest loans.

The Detroit automaker said warranty coverage, service and customer support will continue uninterrupted, and employees and essential suppliers will continue to be paid. GMAC Financial Services said in a statement that it will continues to provide automotive financing to GM and Chrysler dealers and customers. GM will follow a similar course taken by smaller rival Chrysler LLC, which filed for Chapter 11 protection in April. A judge gave Chrysler approval to sell most of its assets to Italy's Fiat, moving the U.S. automaker closer to a quick exit from court protection, possibly this week.

The plan is for the federal government to take a 60 percent ownership stake in the new GM. The Canadian government would take 12.5 percent, with the United Auto Workers getting a 17.5 percent share and unsecured bondholders receiving 10 percent. Existing GM shareholders are expected to be wiped out.

President Barack Obama is scheduled to address the nation about GM's future at midday from Washington, and GM CEO Fritz Henderson is to follow him with a news conference in New York.

Administration officials, speaking on condition of anonymity in advance of Obama's remarks, said they expect the bankruptcy court process to last 60 to 90 days. If successful, GM will emerge as a leaner company with a smaller work force, fewer plants and a trimmed dealership network.

GM revealed Monday that it will permanently close nine more plants and idle three others.

The Pontiac, Mich., and Wilmington, Del., assembly plants will close this year, while plants in Spring Hill, Tenn., and Orion, Mich., will shut down production but remain on standby. One of the idled plants will be retooled to build a small car that GM had originally planned to build in China.

Seven powertrain and parts stamping plants will be closed starting in June 2010, while an additional stamping plant will be idled but remain in a standby capacity.

GM's filing comes 32 days after a Chapter 11 filing by Chrysler, which also was hobbled by plunging sales of cars and trucks as the worst recession since the Great Depression intensified.

The sale to Fiat means Chrysler could be out of bankruptcy within the government's original timeframe of 30 to 60 days. Chrysler's plan gives a 55 percent stake of the new company to a union-run trust for retirees. Fiat gets a 20 percent stake to Fiat that can ultimately grow to 35 percent. The U.S. and Canadian governments get smaller pieces.

The third of the one-time Big Three, Ford Motor Co., has also been stung hard by the sales slump, but it avoided bankruptcy by mortgaging all of its assets in 2006 to borrow roughly $25 billion, giving it a financial cushion GM and Chrysler lacked.

GM will move forward with four core brands -- Chevrolet, Cadillac, Buick and GMC -- and cut four others. The company plans to cut 21,000 employees, about 34 percent of its work force, and reduce the number of dealers by 2,600. GM said it was finalizing a deal to sell Hummer, and plans for Saturn are expected to be announced within weeks.

"There is still plenty of pain to go around, but I'm confident this is far better than the alternative," said Sen. Carl Levin, D-Mich. "It's a new beginning, it's a rebirth, it's a new General Motors."

GM shares fell as low as 27 cents in Monday morning trading, their lowest price in the company's 100-year history, but rebounded to rise 11 cents from Friday's close to 86 cents in midday trading. The News Corp. unit that oversees the Dow Jones industrial average said GM will be kicked out of the index on June 8 and be replaced by Cisco Systems Inc. The index's rules prohibit it from including companies that have filed for bankruptcy.

The bankruptcy filing represents a dramatic downfall for GM, which was founded in 1908 by William C. Durant, who brought several car companies under one roof and developed a strategy of "a car for every purse and purpose." Longtime leader Alfred P. Sloan built the global automaker into a corporate icon. GM first sought help from the Bush administration and Congress last year as it was in the midst of being staggered by $30.9 billion in losses and seeing its cash resources shrink by more than $19 billion.

Consumers, worried about the economy and the future of GM, shied away from the company's cars and trucks this year even after President George W. Bush promised loans and Obama followed through with billions more in assistance -- plus a stiff set of new requirements GM was ordered to meet.