DETROIT — After months of struggling to stay alive on government loans, Chrysler succumbed to bankruptcy yesterday, pinning its future on a top-to-bottom reorganization and plans to build cleaner cars through an alliance with Italian automaker Fiat.

The nation's third-largest car manufacturer filed for Chapter 11 bankruptcy protection, with ambitions to emerge in as little as 30 days as a leaner, more nimble company, probably with Fiat as the majority owner. In return, the federal government agreed to give Chrysler up to $8 billion in additional aid.

"It's a partnership that will give Chrysler a chance not only to survive, but to thrive in a global auto industry," President Obama said.

Starting Monday, Chrysler said, it will close all its plants until it comes out of bankruptcy. At least three Detroit-area factories sent workers home yesterday after suppliers stopped shipping parts over fears they would not be paid. CEO Robert Nardelli announced he would step down when the bankruptcy is complete and take a post as an adviser with Cerberus Capital Management LP, which will give up its 80 percent ownership of Chrysler under the automaker's plan.

Chrysler's bankruptcy is the latest step in a reordering of the U.S. auto industry, which has been hit by higher fuel prices, the recession and changing customer tastes.

Lee Iacocca, the retired chairman and CEO who led Chrysler through a government bailout in the late 1970s, said it was a sad day.

"It pains me to see my old company, which has meant so much to America, on the ropes," he said in a written statement. "But Chrysler has been in trouble before, and we got through it, and I believe they can do it again."