DETROIT (AP) _ General Motors Corp., trying to trim its work force without layoffs, has reduced the age at which some salaried employees can qualify for an early retirement program.

Under a program unveiled Thursday, some U.S. and Canadian white-collar workers can retire at age 50.

The early retirement offering is GM's second this year. An earlier program allowing retirement at age 53 with 10 years of service was so widely accepted that GM moved up its goal of cutting 20,000 salaried employees from the end of 1994 to the end of 1993.

Under the new plan, GM workers in overstaffed units can retire at 50, while others can leave at 52 with the same benefits, if they have 10 years of service. GM declined to say how many workers would be eligible. The automaker's mandatory retirement age is 65.

The new program is good through the end of 1992, Richard O'Brien, vice president of corporate personnel, said on GM's internal Newsline.

Some analysts believe GM may have to resort to layoffs to cut its employee rolls enough to match lost market share and the shrinkage of its business base.

''It's always nasty in a downsizing,'' said Joseph Phillippi, an auto industry analyst with Lehman Brothers Inc. in New York. ''Some of GM's executives may take this chance just to walk away before they get blown away.''

GM is cutting 54,000 hourly jobs by 1995. It is discussing with the United Auto Workers union a new round of early retirements that could help reach that goal sooner.

GM's loss of $4.45 billion in 1991 was a U.S. industry record. It is expected to lose about $1 billion this year, its third consecutive year of losses.