WASHINGTON -- President Barack Obama will announce on Monday the bankruptcy of General Motors Corp., launching a complicated, $59-billion effort to prevent the century-old juggernaut of American manufacturing from collapse.

•FACT SHEET: White House on the new GM

Backed by its unions, large bondholders, and the governments of the United States, Canada and Ontario, GM will file in New York a painful plan to cleave itself into a lean, government-owned automaker pared down to compete in a sputtering U.S. market.

As part of the bankruptcy, GM will spell out 14 plant closings expected to affect 21,000 jobs, and additional cuts among salaried workers.

• PDF: A visual look at manufacturing job losses

President Barack Obama will address the nation from the White House at 11:55 a.m. on his rescue of the nation’s largest automaker, planning to infuse $30.1 billion to pay for the bankruptcy and emergence of a new GM, on top of the $19.4 billion in loans that officials say did little but delay the reckoning by a few months.

Obama planned to speak to Michigan members of Congress about the bankruptcy Sunday, which will rank as one of the largest and most complex cases ever.

Even though its decline can be measured in decades, the magnitude of GM’s retreat is still staggering. Where one of every two vehicles sold in the United States came from a GM factory through much of the 1970s, the automaker held just 19% of the market through the first quarter of this year. After holding the title of world’s largest automaker for 77 years, GM is now hocking a majority stake in its European operations and paring expansion in the foreign markets it once targeted as its future.

“This is GM’s moment to get the company right,” said Rebecca Lindland, analyst with IHS Global Insight. “They’ve been constrained by legacy costs and labor agreements, but now they can right-size the company to make money. It’s not a guarantee, but they’ve got no excuses left.”

GM Chief Executive Officer Fritz Henderson will speak in New York today following Obama’s comments. Among the new details he’s expected to discuss will be the appointment of restructuring expert Al Koch of Southfield-based AlixPartners as a chief restructuring officer, people familiar with the plan said Sunday.

While Obama and Henderson will highlight the opportunities GM has been granted, and its potential to rebound after shedding most of its debt, today’s bankruptcy will indelibly mark the lowest moment in the company’s 100-year history.

GM’s shares, having peaked in 2000 at $93.62, could be taken off the New York Stock Exchange today after closing Friday at 75 cents, with the company’s bankruptcy plan expected to render them worthless.

GM’s bankruptcy strategy as designed by the Obama auto task force will call for the automaker to sell most of its assets to a “new” GM, with the remaining assets of the company sold off to satisfy debts and claims. The sale could happen in 60 to 90 days, allowing the new GM to escape bankruptcy while the wind-down of the remnants could take years.

It’s the same strategy employed by the administration in its rescue of Chrysler LLC, whose plans for a sale to Fiat S.p.A. was approved by the same New York bankruptcy court late Sunday. The new Chrysler-Fiat partnership could emerge by June 15.

In return for cancelling all but $8.8 billion of its $49.5 billion in loans, the U.S. government will own 60% of the new GM – a share administration officials said was taken “reluctantly.” The Canadian government will lend GM an additional $9.5 billion, taking a 12.5% stake in return.

The health-care trust fund for UAW retirees will hold 17.5%, with the promise of buying an additional 2.5% should the company succeed. While the trust fund will cut health care benefits for retirees, the pension plans for hourly and salaried workers will be preserved in the new firm.

Bondholders carrying 54% of $27.2 billion in unsecured GM bonds agreed to a deal with the Obama administration Saturday to drop their opposition of GM’s bankruptcy plan in return for a stake of 15% in the new GM, with rights to buy an additional 10%.

The vote lessens but will not eliminate the challenges GM will face in bankruptcy court from debt holders and other creditors. Large GM bondholders had backed the sweetened deal from the administration, saying the government’s decision to swap most of its loans for new GM equity left the company with a workable amount of debt.

But individual bondholders were shut out of the offer, made with less than three days notice, and several said they would attempt to fight in bankruptcy court, arguing the plan unfairly enriches the UAW health-care trust fund.

“Individual investors have been systematically excluded from the negotiating table in the restructuring of one of America’s storied icons,” said GM Bondholders Unite in a statement.

The administration said the plan should allow GM to break even in a U.S. market of 10 million vehicle sales, roughly what the industry expects this year. While the government plans to avoid day-to-day decisions, it did vow to protect the investments of taxpayers, and warned that GM’s first federal rescue would also be its last.

“One never says never,” said a senior administration official Sunday, “but this is it for support for GM.”