It was a slight shock to walk out into the Hartke Theatre courtyard after Act 2 of the Summer Opera Theatre's "Die Fledermaus" last night. It was, in fact, a dizzying plunge from New Year's Eve in 19th-century Vienna to a hot summer evening in Reagan-era Washington. Identification with the vivid proceedings on stage was so complete that one needed a moment to adjust to the drab reality outdoors.

The Act 2 finale was in many ways the show's climax: first the brilliant champagne chorus, then the tunefully sentimental "Bru derlein" chorus ("Happy Days" in Garson Kanin's English translation) when everyone on stage suddenly seemed deeply in love, followed by the final waltz and the drunken exit of Eisenstein the prisoner and Frank the jailer.

It was splendidly staged, with Orlofsky and Falke riding on a swing far above the stage, champagne glasses raised everywhere, brightly colored gas balloons that seemed to appear out of nowhere and a glitter ball sprinkling light through the audience. The superbly costumed chorus sang its music beautifully and then exited through the audience -- but first it had supplied, with its bodies and costumes, a bright, happy stage picture into which one yearned to slip.

But this was only one outstanding moment in a performance that had a host of others.

In many ways, conductor William Noll and stage director John Lehmeyer collaborated on a classic "Fledermaus," a production stripped of accretions that have been added through the generations and become almost ritual elements. The most notable change was the reduction of Frosch's drunken Act 3 monologue to the minimum found in the original script.

Similarly the comic French dialogue in Act 2 was clipped to a couple of phrases, and the "gala" hors d'oeuvres that are so often slipped into the party scene were omitted. The Orlofsky in this production did not go on at boring length about how bored he was -- and, in fact, he soon began visibly enjoying the fun, like everyone else.

There was one radical innovation. Some of the time saved by trimming Frosch's monologue was used to introduce a new routine that deserves to become traditional. During Frank's hangover sequence in Act 3, when the orchestra begins playing a waltz as though everyone in the pit were drunk, a pink elephant (complete with tutu, toe shoes and bright red painted nails) dances onstage and has a hilarious waltz with Frank.

Otherwise, this production stuck quite close to the original concept of the operetta, particularly in Act 3, where the denouement is often given short shrift to make time for irrelevant comic turns. Here, Eisenstein's final bit of role-playing (when he pretends to be a lawyer) and the last stalemate (when each of the spouses triumphantly flaunts evidence of the other's betrayal) were brought into a kind of focus that is seldom found in performances making a mad, last-minute dash for the final curtain.

Without doubt, the star of the show was soprano Myra Merritt, who sang the part of Rosalinde with splendid tone and agility while displaying a strong comic flair. Those who saw her performance as Musetta in the Metropolitan Opera's "La Bohe`me" a few seasons ago are aware of her comic talent, but nothing she has done before is quite like her masquerade as a Hungarian countess in Act 2, getting off such lines as "vot a shtunnink votch" and singing her czardas as well as I have ever heard it sung.

Tenor Philip Bologna, like Merritt one of the company's regulars, gave a brilliant performance as the tenor Alfredo, ardent and silver-toned and extremely funny. He could probably make a career of this role in various opera houses, though this would mean the loss of a fine Alfredo, Pinkerton, et al. Carla Connors, who was Papagena earlier this season in the Summer Opera's "Magic Flute," is a brilliant Adele, particularly in the Act 2 laughing song, where male dancers hoist her on their shoulders. Less vivid but commendable work was also done by Howard Carr as Eisenstein, Deidra Palmour as Orlofsky, and Alex Helsabeck as Falke. Supporting roles were well filled by Richard Tappen, Dana Dowd and Charles Gregan. Noll's conducting was brisk and bright, but in some passages he might have slowed down to let the music breathe a bit more. Miguel Romero's sets were functional and evocative and might be recycled into a "Rosenkavalier" if the company chooses to do one.