When Reader's Digest bought a suburban Virginia computer information firm called Source Telecomputing Corp. two years ago, the staid Pleasantville, N.Y., company unwittingly entered the world of sexual swingers.

The Source is a service that allows home computer users to summon, by telephone, an array of routine information services such as United Press International news and sports stories and stock market quotes. But by using some of the Source's other features that allow subscribers to talk with each other, some customers have found a way to pursue more private pleasures.

For example, there's "gorgeous and adventurous" Ginger in Houston who is into "intimate apparel, sex and romance." Phil and Liz of Maryland advertise an interest in "couples, sex" and Plato's, presumably not a reference to the philosopher but to the notorious New York swingers' club. Carrie, Linda and Nancy in Florida express an interest in drugs and sex in language not suitable for reprinting in a family newspaper, or Reader's Digest, for that matter. Gays seek companions. A Coral Gables man who describes himself as a "well-built surfer with blond hair and blue eyes" solicits female surfing partners for "a religious and wholesome relationship . . . Please send a recent 8x10 glossy photo of your surfing form."

For a one-time hookup fee of $100, more than 22,000 home computer users in North America (about 10 percent of the subscribers live in the Washington area) subscribe to the Source and are billed for each minute of use. About 1,500 new subscribers join each month, according to a Source representative.

Using home video terminals and a telephone hookup, subscribers can, in addition to UPI and stock market services, summon airline schedules and reserve tickets, practice foreign languages, play blackjack and dozens of other games, perform complicated math problems, read restaurant and movie reviews, send and receive electronic mail and use hundreds of other information services.

But in a couple of categories, users can advertise for dates and even talk to each other with computer terminals via the Source. It is the dating section of an electronic "bulletin board" that a Source editor checks each day, deleting any "material we consider objectionable," according to Source executive editor Mary Lou Forbes. "We do monitor what we consider explicit obscenity."

But another category called "DISEARCH" has missed the scrutiny of Source management. A user can request a listing of all subscribers who share a common interest by typing in a key word. The word "sex" recently summoned about 65 people who included sex as their interest, along with more mundane categories such as scuba diving, travel, chemistry and commodities. Codes along with the names permit subscribers to communicate. According to the Source's public relations director, Mike Rawl, a couple of subscribers have gotten married after meeting each other through their home computers.

But Rawl expressed surprise at the contents of the "DISEARCH" file and said he would conduct an immediate review. A public relations spokesman for Reader's Digest in Pleasantville -- which recently denied reports that the Digest wanted to sell the Source because it was not yet earning a profit -- expressed similar surprise but joked, "This may be one way to sell the service."