DETROIT (AP) _ A nationwide mailing next week of 500,000 booklets to some autoworkers is the latest step in a joint AIDS education program run by General Motors Corp. and the United Auto Workers union.

''Our main message is that you can't get AIDS through casual contact in the workplace,'' said Maureen Moll, a consultant to the program. ''There's a lot of fear out there, and we're trying to educate people on how AIDS is transmitted and on what they have to do to protect themselves.''

The 36-page color, magazine-size booklet is to be mailed beginning Monday.

It contains articles about helping a relative deal with the disease, how to tell children about acquired immune deficiency syndrome, understanding the disease in the workplace, research and financial help for victims and their families.

Trish Houtteman, co-coordinator of the UAW-GM AIDS Education Program which developed the booklet, said GM employees and their families account for about 2.3 million people, or about 1 percent of the U.S. population.

Houtteman said because of confidentiality rules, she doesn't know how many GM employees have AIDS. The Centers for Disease Control in Atlanta said this week it has received reports of 79,389 AIDS cases nationwide, resulting in 44,950 deaths.

If federal projections about the growth of AIDS are correct and 1 percent of those people are GM employees, Houtteman said, the automaker could be faced with insuring 2,500 AIDS victims by 1991.

The cost of that could run into billions of dollars, said Ted Miller, the program's other co-coordinator.

''This wasn't done just because of economics, I can assure you,'' said Miller, assistant director of the UAW's GM Department. ''It's more a question of helping people.''

The booklet also contains frequently asked questions and answers about AIDS, a fatal disease that disables the body's ability to fight infections.

The booklet is part of a larger program that also has included a conference by video in February among about 2,000 company and union officials, a nationwide mailing of a six-page booklet earlier this year and training for medical and safety personnel and counselors at all GM plants.