I suppose any show that helps get dinner theaters out of the well-worn rut into which most of them have tumbled is welcome these days. While there's nothing remotely adventurous about "the Student Prince," I can't recall ever having seen it before on the local circuit.

It is mildly ironic that such an old warhorse could qualify as a novelty, yet that's the case at the Harlequin Dinner Theatre, where the Sigmund Romberg operetta is holding forth this month. Director Dallett Norris has pruned the work severely, so that the two brief acts move as quickly as possible from one soaring song to the next. This is what you might call "the Student Prince's" biggest hits version, but then melody has always been the show's strong suit.

The story is, well, what it is: a schmaltzy account of Prince Karl Franz's halcyon days as a student in Heidelberg and his romance with Kathie, the pretty waitress at the Inn of the Three Golden Apples, that comes to an end when he ascends to the throne. It's easy to make fun of, but the Harlequin cast approaches the material with enough verve and innocence to hold cynicism at bay. And the old standbys -- "Drinking Song," "Deep in My Heart," "Serenade" and "Golden Days" -- are sung robustly and with feeling.

What periodically lifts the show above a kind of pleasant competency is the beguiling performance of Gay Willis as Kathie. Every now and then, dinner theaters spring on us young talents who are clearly destined to move on. Willis is one of them: an attractive woman with an enchanting soprano voice, a graceful stage presence and a sweetness that is never for a moment cloying. She is obliged to protray some fairly hoary sentiments -- from the blushing timidity of her first encounter with the prince to the brave nobility she brings to their final parting. She makes them all perfectly believable.

If Pete Herber is a bit stiff as the prince, he, too, has a commanding singing voice, and his duets with Willis bring out the best in him. The other cast members are not so well matched to their roles, but let's face it, those roles aren't much. "The Student Prince" depicts a never-never land, where brotherhood is found in a stein of ale and romance in the silvery moonlight. Royalty was never like this. Nor, for that matter, was the peasantry. But as long as the characters are singing Romberg's indestructible score, you're at least willing to pretend.