Part of the excitement of opera in turn-of-the-century America is the increasing abundance of new work to be seen, to be heard, to be digested.

Everyone is doing it, in one form or another, but few premieres have had the sex appeal of Tennessee Williams' "A Streetcar Named Desire" set to music by Andre Previn at San Francisco Opera last month.With the vivid personalities the playwright conjured up for his play - two of whom are virtual icons in America's theatrical imagination - the smoky, heat-filled ambience of New Orleans and the tragic pull of the narrative, the play is a natural for lyric muse. And while ballets have been based on the Williams text, no one attempted an opera until Previn.

Some have called Previn's opera the best in more than two decades, while others have decried its too-free adaptation of mixed musical sources and lack of Southern verisimilitude.

Except for a weak second act that just trips along, anxious to keep up with the flow of Williams' words, the opera has a firm grip on our consciousness with telling characterizations, a score that punctuates with color and exclamation points and moments of stark horror and sadness. Previn gives Blanche all the arias the deluded lady of the Old South could ever want, but none to Stanley because the composer thought the rough and tumble guy wasn't the sort to sing arias. Previn is sparse with duets, curiously, but those few work with surprising power.

Indeed, Previn has written an opera that sits nicely in the ear. It can move speedily along, but then slow down to savor the moment. The composer has taken our pluralistic age at its word and borrowed from many, including two 20th-century Russians, Prokofiev and Shostakovich, bits of Richard Strauss and occasional hints of jazz, not well played by the orchestra. On occasion, Previn stoops to movie music cliches. Philip Littell's libretto is faithful to Williams' text but does not illuminate it.

Michael Yeargan's set - the Kowalskis' two-room apartment - evokes the French Quarter deftly. For variety, it revolves. Thomas J. Munn's lighting design is equally effective.

One could not ask for a better cast: Renee Fleming as Blanche; Rodney Gilfry, Stanley; Elizabeth Futral, Stella; and Anthony Dean Griffey, Mitch.

Fleming's Blanche sits at the very heart of the opera. She is given a good share of the best, the most poetic music, which she delivers with eloquence. Admittedly, she is neither Jessica Tandy, who created the role on Broadway, nor Vivian Leigh, who appeared in the movie, but she sings with beauty of tone and acts in an appealing manner.

Gilfry looks like a Stanley, big and muscular and brash. He has a strong stage presence, full of masculine pride and threatening gestures. But he is given little to do vocally. Futral has a sweet soprano and a sweet, loving presence, which makes her a good counterpoint to her older sister, Blanche, and her husband, Stanley. Griffey makes for a pitiful, and well-sung, Mitch.

There has been considerable criticism on how well the opera, and the accents of its principal characters, suggest the South. On that subject, I cannot offer an opinion. But I did ask the opinion of the music critic for the Times-Picayune, New Orleans' leading newspaper, at the performance. He said he thought the negative comments were not justified.

The orchestra, conducted by Previn, was disappointing.