"A Night in Venice," which opened the 12th season of the Summer Opera Theatre Sunday night at the Hartke Theatre, musically ranks close to the top three operettas of Johann Strauss Jr.: "Die Fledermaus," "Wiener Blut" and "The Gypsy Baron." Its problem is a crazy, mixed-up libretto, but the music and the Summer Opera's sparkling production make the plot's absurdities seem unimportant.

Like many operettas, this one's chief business is to split up young couples, scramble their attempts at communication, confuse their identities, and finally get them back together in time for a happy ending. Two couples will do nicely for most purposes, and three are manageable. "A Night in Venice" ends up, just before the final curtain, with more -- four couples if you count only those involving solo singers; 15 if the couples in the chorus are included, as they loudly insist they should be.

In the Summer Opera production, a seemingly inexhaustible stream of delicious (sometimes Italian-flavored) Strauss melodies is performed by a very able cast of young singers, a vocally bright, theatrically energetic chorus and a handpicked orchestra well conducted by Kim Allen Kluge. The stage direction by John Lehmeyer raises campiness to almost unimaginable levels. The sets by John Michael Deegan and Sarah G. Conly are splendidly Venetian with gondolas everywhere, St. Mark's Cathedral as an atmospheric painted backdrop, sumptuous palace interiors and a plaza full of pigeons that actually flutter off on cue. Lehmeyer's costume designs, some of which have a strong commedia dell'arte flavor, are also effective.

Standing out among the male singers, for comic as well as vocal talent, is William Killmeier, who portrays Guido, Duke of Urbino, as a sort of homme fatal, fascinated by his mirror. In a superb parody of any number of movie scenes, Act 2 opens with the duke taking a bath in a large metal tub overflowing with bubbles. The tub is equipped with handles like a sedan chair and is carried off by four footmen after the ladies of Venice (properly cloaked and masked) give the duke a thorough inspection and one of them scrubs him a bit. This, like the chaise longue (designed for seductions) that keeps rolling across the stage, the trapeze, the pigeons, the (nonexplosive) fireworks and the grotesquely long-nosed mask that is taken off to reveal an equally long-nosed face underneath, has nothing much to do with the plot, but along with the waltzes, polkas, drinking songs, love songs etc., makes "A Night in Venice" a pleasant evening's entertainment.

The two leading ladies are both vocally excellent and wonderfully contrasted: Myra Merritt brings her usual elegance to the role of Annina and Jody Rapport is splendidly earthy as the maid Ciboletta. In a supporting role, Phyllis Burg sometimes makes one think of Mae West. Karl Laird is superb as the barber Caramello, and excellent comic and vocal performances are given by Fred Frabotta as Pappacoda the macaroni cook and Andrew Wulff as Senator Delacqua.