A spoof of Wasps and old money

Preppies Musical comedy with book by David Taylor and Carlos Davis, music and lyrics by Gary Portnoy and Judy Hart Angelo. Directed and choreographed by Tony Tanner.

Off Broadway has launched its musical-comedy season at the handsomely refurbished Promenade Theatre with a harmless attempt to spoof the shows of the '20s and '30s, when librettos were sillier and stage life willy-nillier. ''Preppies'' draws on pop jargon and the affluent society for a tale about the son of a maid and a manservant whose parents allow him to be adopted by a dying billionaire. The billionaire thereby acquires an heir to inherit the vast estate (including Central Park and Wyoming) that would otherwise go to grasping rivals in the family.

The plot is a predictable as the jokes about Wasps and old money. Early on in the 21-year saga, somebody remarks of the juvenile pretender that ''he's not going to kindergarten - he's going to be interviewed for kindergarten.'' And so on through summers in Maine, prep school at St. Grottlesex, Yale, and the inevitable deb parties leading to the inevitable engagements.

The score ranges from the hummable to the ho-hummable. For the fetching ''Summertime,'' director-choreographer Tony Tanner has devised a novelty tap routine performed in scuba flippers. As the juveniles, Bob Walton and Kathleen Rowe McAllen duet nicely in ''Our Night,'' while Michael Ingram and Beth Fowler, as the sacrificing domestics, deftly sing and dance their way through ''We've Got Each Other.'' The indispensable David Sabin plays a succession of roles, from the billionaire to a major-domo. Dennis Bailey's snake-in-the-grass comic villain raises ''Preppies'' to gift-wrapped hilarity in Mr. Tanner's inspired staging of ''Bring on the Loot.'' The snazzy production was designed by David Jenkins (scenery), Patricia McGourty (costumes), and Richard Winkler (lighting).