The Kennedy Center's new intimate opera was beautifully launched last night as the Terrace Theater proved its versatility in housing Mozart's "The Impresario" and Weber's "Abu Hassan."

One lavishly handsome stage picture followed another as the operas unfolded. In a conceit that was often tedious in Mazart but unfailingly charming in Weber, the former was used as the framework for presenting the latter. This can work very well, since Mozart wrote only an overture, two arias, one trio, and a final quartet for his short curtain-raiser, necessitating in his own day and ever since, the addition of some topical dialogue.

The problems arose with the decison to shift the the action from Mozart's day to Washington, D.C., the specifically the stage of the National Theater, in the 1880s, during the presidential term of Chester A. Arthur. Local gags mingled freely with sight gags in references to Ebbitt's Grill, Peacock Alley in the Willard Hotel, and "Ah, Baltimore" which, for some reason got a laugh.

Often the text, provided by Hugh Wheeler, died of malnutrition in lines that sounded like the plays Samuel French used to peddle to high schools 50 years ago. No one questions that the original libretto Mozart set was a dog. But a new one with overdoses of ham is just as much as a drag.

There is fun at times, but no Mozart opera should go for 15 minutes after the overture before someone sings something. This one does. Once the arias (sung by rival sopranos) arrive, things pick up dramatically as well as in the music. And when Faith Esham, in the invented character of a retiring rehearsal pianist, stepped up and sang the interpolated "Ruhe sanft," from Mozart's "zaide," the house was hushed for the loveliest singing of the entire evening.

Wheeler has introduced 10 speaking roles into the farce; the burden is far too great and much too long. But a happy note: The company, actors and singers alike, is marvelous. In Jack O'Brien's witty, imaginative and lively staging, they do everything they can with what is too often a drag. What might well last three quarters of an hour goes on for five quaters.

There are very few reservations on the musical side of things. Music director of the new opera theater John Mauceria provides ideal orchestral support for both pieces and superb accompaniment for every moment of song. The acoustics of the Terrace Theater remain as dry for opera as they are for chamber music and concerts. Thus the violins sound a bit thin and raw. But there was a lovely cello solo and notable clarinet and bassoon passages.

Against luxurious sets and in elegant costumes, both by Steven Rubin, Esham, starring as Weber's Fatima as well as in Mozart, is a dream of a singer, with notable style and fantastic command of tone. And like all her colleagues, she showed up, in the close range of the small theater, with strong acting gifts.

Raymond gibbs, doubting as Mozart's tenor and in the title role of Abu Hassan, sings with polished ease. The top of his voice is wide and uncovered, giving out much more sound than he needs in the theater, which is at the opposite end of the world from the Metropolitan Opera where he sings regularly. He ought to make some adjustment for the difference.

Harry Dworchak is a standout singing Mozart's bass and later Weber's Money Lender, making the most of the cramped cupboard in which he spends much of his Weberian time. As the rival sopranos in Mozart, Janice Hall and Claudia Cummings are adequate, though neither wins prizes for accuracy.

The over-large acting troupe includes several top-notch players of whom Jack Aranson deserves very special praise. Brought in only four days ago to play the long role of the impressario, he had the part completely in control and turned in a virtuoso performance, ham and all. The most memorable character in the additions to Mozart is that of Marvin Trott, "a local playwright." Richard Bauer, familiar to Arena Stage audiences, made the part a dazzling, brilliant personal success in a Bumbling, Mumbling, twisting display of wonderful pointed humor. If ever this new version of "The Impressario" were mercifully shortened, that part should be kept intact as long as Bauer will play it.The Mozart-Weber bill will be repeated on alternate nights through July 26. CAPTION: Picture, Raymond Gibbs and Faith Esham, by Margaret Thomas - The Washington Post