DETROIT  General Motors is living on borrowed time, spending more than $2 billion in cash a month and lobbying for a government bailout to keep it out of bankruptcy.

And for about 100,000 of its white-collar retirees, time is about to run out on G.M.’s gold-plated medical benefits.

To conserve its dwindling cash reserves, G.M. is eliminating lifetime health care coverage for its legions of retirees at the end of this year, leaving people like Ken Hewitt to fend for themselves in deciding how to cover their doctor’s bills and prescription drug costs.

“Everybody felt like they were set for life,” said Mr. Hewitt, 81, who retired from the former Chevrolet Engineering Center in 1982 and lives north of Detroit. “It’s been difficult, but the information they’ve given us has been beneficial. Still, when you get to be our age, it’s tough to make any big changes like that.”