Tuneups and turnips

In theater, too, summer is a time of lighter fare. People want to escape, to dream, to laugh, so goes prevailing sensibility, and plays presented by stock companies are as substantial as sea foam. While occasionally serious work is done, you are a lot more apt to see ''Barefoot in the Park'' than ''King Lear.''

While the stock theaters this summer seem to be choosing more family musicals (''Joseph and the Amazing Technicolor Dreamcoat'' is playing in 13 spots) and fewer sex comedies like ''Once Upon a Mattress,'' there continues to be a market for empty and raunchy fare.

One such show, ''Pump Boys and Dinettes,'' ran on Broadway and is now roaming the stock circuit, playing recently at the North Shore Music Theatre in Beverly. For all its country feeling, ''Pump Boys'' is undergirded with the steel spokes of commerciality.

It dishes up the usual country/rock/calypso/gospel stew of songs about life in a roadside diner/gas station. Every stereotype about loose, sassy waitresses and lazy, good-ole-boy pump boys is twanged on, and the sexual bantering between them flies faster than windshield wipers in a storm.

To make the show sell, writers John Foley, Mark Hardwick, Debra Monk, Cass Morgan, Jim Wann, and John Schimmel tossed in a couple of sentimental songs about family relationships, and a few just-plain-fun numbers (''Farmer Tan'' really was a kick). It's kept moving so fast that the audience doesn't have time to realize that it has no more than a nibble of the real lives of the characters.

Don't get me wrong, most of ''Pump Boys'' is harmless and fun. It's a revved-up show, and the performers' singing and playing are outstanding. But it's a nice concept that is taken little further than a dune buggy bumping over the ruts of stereotypes and titillation that the ''Hee-Haw'' TV show has.

''Pump Boys'' is playing now at the Cape Playhouse in Dennis, Mass., through Saturday; the Ogunquit Playhouse, Ogunquit, Maine, Aug. 13-18.