Among Joseph Papp's legacies to the theater, we can now count the renewed popularity of "The Pirates of Penzance." The Gilbert and Sullivan operetta has always had its share of partisans, of course, but it was Papp who conceived the notion of putting rock stars in some of the lead roles when he revived the work a few years ago. Not only was his production a rambunctious delight, but the good word carried far and wide.

As a result, we are now in for waves of "Pirates," the first of which has just broken at the Harlequin Dinner Theatre in Rockville. Lord knows, the dinner-theater repertory is so severely restricted that the addition of Gilbert and Sullivan to the list has to be considered welcome. This production, while a little green and not quite as sharp as it could be, is indeed likely to please the family trade. And it does have this distinct advantage: It's not "The Sound of Music."

In fact, the Harlequin production, directed by William Wesbrooks, has several assets: a pirate king, nicely played by Jamie Zemarel with the swashbuckling klutziness that Kevin Kline seems to have imprinted permanently on the part; a vigorous Fred (he's the apprentice who wants out of the pirate band), sung with great spunk by Tom Allen; a sweet Mabel in the person of Gay Willis; and a major general, Spencer Harrill, who is not yet up to full speed on his patter song, perhaps, but is clearly within grasp of it.

Unlike the company that played the National last season, the Harlequin cast is properly mindful of its diction, so that Gilbert's playful words get as much attention as Sullivan's lilting melodies. And the sets, if modest, strike the right pastel notes. The chief drawbacks are a contingent of the Keystone Kops, reduced to four and singing like two, and a nursemaid (Sharon Ammen) of less-than-convincing comic talents. Still, this production manages enough moments when the sprightly nonsense all comes together to pass muster.

As a rule, our local dinner theaters tend to go with those musicals that are already widely known to the general public. Broadway, however, is producing fewer and fewer of them these days. Hence a bind that can only grow tighter in the future. No doubt we are seeing "Pirates" at the Harlequin because it was a recent Broadway hit. Still, it could be a modest breakthrough, if other Gilbert and Sullivans followed in its joyful wake.

THE PIRATES OF PENZANCE. By Gilbert and Sullivan. Directed by William Wesbrooks; sets, Jeffrey Schneider; musical direction, Thomas Whiddon; costumes, Rayanne Miller; lighting, Thomas Lawrey. With Jamie Zemarel, Tom Allen, Gay Willis, Spencer Harrill, Michael Young, S. Noel Dunn, Sharon Ammen. At the Harlequin Dinner Theatre through April.