The Summer Opera Theatre opened its seventh season last night with "Ariadne auf Naxos," the richest, most intricate mixture of high tragedy and low slapstick in opera. It was stylistically the trickiest and musically the most challenging work yet attempted by this young, financially limited company, and it was a triumph. The few tickets remaining for the Friday and Sunday performances at the Hartke Theatre will be worth fighting for.

"Ariadne" tells the story of an evening's entertainment, beginning with dinner and ending with fireworks, in the home of the richest man in 17th-century Vienna. A new tragedy, by an idealistic young composer, is to have its first performance, telling the story of Ariadne, who was abandoned by Theseus on a desert island and (after a long, baroque lamentation) rescued by Bacchus. Also on the program is a semi-improvised Italian commedia dell'arte, "Faithless Zerbinetta and Her Four Lovers."

At the end of Act 1, which is full of backstage bustle, confusion and intrigue, the players are told that dinner is late, the fireworks must begin at 9, and the two completely incompatible pieces must be performed simultaneously. That performance, sublime and ridiculous in the same breath, is Act 2 of the opera.

The music's vocal demands include a dramatic soprano and tenor of Wagnerian power who can also do comedy, a comic coloratura whose voice can soar light as a feather high above the treble staff, a mezzo who can put on trousers and (as the Composer) remind the audience of Mozart, as well as a half-dozen supporting players with a flair for slapstick and ensemble singing. Orchestrally, it needs a richness and variety of texture comparable to "Der Rosenkavalier," though a bit lighter. And its curious second act calls for a high level of clarity, deftness and versatility in stage direction. These are all joyfully, triumphantly present in this production.

This "Ariadne" is above all an ensemble performance. There is a lot of impressive solo work, particularly from Regina McConnell (Ariadne) and Anne Johnson (Zerbinetta), and nearly everyone in the cast has at least a significant moment or two. But the interactions among the performers, musically and theatrically, outweigh the work of any individual in generating the work's harmonious, tightly organized and brilliantly focused total effect.

Nearly 10 minutes of silent stage business set the opera's framework before the first note of Richard Strauss' score or the first syllable Hugo von Hoffmansthal's libretto is heard. The Wig Master, primping his hair in a corner, hums (symbolically) bits of Mozart (the Queen of the Night's music and "Batti, batti") that make one wonder about his sexual orientation.

The singers who will represent three nymphs in Act 2 mime the jealousies that will later mark their performances in the opera-within-an-opera. There is much traffic around the dressing room of the amorous Zerbinetta. Then the music begins, and the libretto kicks into action, much enriched by the unwritten prologue, which is stage director John Lehmeyer's work and a touch of genius. Similar genius is show in small touches throughout the production -- notably when the three nymphs (splendidly performed by Mary O'Connell, Linda Iannuzzi and Yvette Lewis) try to upstage one another and the prima donna.

Michael Morgan's conducting (with the best orchestra I have heard so far in the Summer Opera) achieves comparable levels of subtlety and attention to fine detail. He is clearly developing into a major talent, though it took him a few minutes to establish ideal balance of voices and orchestra in Act 1.

There are other imperfections, of course; this "Ariadne" is peformed (as it should be, particularly Act 1) in English, but quite a few of the words are blurred, notably when the women are singing in their upper registers. Still, enough of the text gets through to provide intense enjoyment.

Daria Gerwig (as the Composer) is often splendid but uneven, her low notes sometimes lacking strength and focus. Daniel Tomaselli (as the Tenor and Bacchus) has a voice of great power but little subtlety, and Donald Ronci was more effective in his Act 2 ensemble singing than his Act 1 solos. But these were small, momentary problems in a first-class performance.

Highlights included particularly the spectacular singing of Johnson and McConnell in the virtuoso music of Act 2, Alan Baker's stalwart work as the Music Master (including a comic touch when he appeared in the pit to "conduct" the opera-within-an-opera), the fine ensemble work of Richard Byrne, Howard Carr, Vladimir Ekzarkhov and Donald Ronci as Zerbinetta's four companions and the brilliant cameo roles of Todd Sieweret as the Major Domo and James Harp as the Wig Master.