Renata Scotto's "Madama Butterfly" is one of the celebrated characterizations in opera today. Last night her performance of it with the Met at the Kennedy Center was vocally assured and dramatically electric.

Alone she triumphantly carried what was otherwise a mostly mediocre evening.

Scotto's Cio-Cio-San begins by throwing out the common stereotype of Butterfly as the poor little waif who doesn't seem to know what's going on as she is repeatedly bludgeoned by the betrayals of her Ugly American naval officer, the callous Benjamin Franklin Pinkerton.

Scotto's Butterfly knows exactly what is going on, better than anyone else in this sad affair. By the beginning of Act Two--the crucial act--she has already matured into a woman who has learned to live honorably with desperation. She has no choice. As the savage extent of her plight gradually unfolds, she moves from panic to despair, but it is only when Pinkerton arrives with his American wife to take away his Japanese child that this Butterfly is crushed, in suicide.

Scotto moves from strength to strength. She has the superb insight of taking the cliche'd naivete out of that most famous aria, "Un bel di, vedremo," by singing of that fine day when Pinkerton will come as a gesture to comfort her frightened maid, Suzuki. She finally gets Suzuki off to rest and returns to end the aria with an anguished sob as she glances at the photo of the officer and collapses. There is no suggestion that "Un bel di" is, as usual, merely a foolish young girl's pipe dream. A dramatically problematic aria becomes a moment of gripping drama.

The second act duet with Sharpless, the American consul in Nagasaki, was a model of how subtle dramatic punctuation will say much more than explicit confrontation--as Butterfly reads his intent when he bumbles away, fearing her reaction to his grim message. And baritone Mario Sereni, as Sharpless, provided the one superior male performance of the evening.

As for Scotto's vocal condition--in light of her exertions as "Norma" last week--the news is good. The voice is not as free as it was the '60s when she made her gorgeous first recording of "Butterfly." But the voice remains essentially right--warm, flexible and well-placed. The high notes show her age, but with perhaps one exception there were none of the disconcerting breaks of register from last week.

Butterfly's companion, Suzuki, was well sung and splendidly acted by Claudia Catania.

The less said the better of tenor Giuliano Ciannella as Pinkerton. It was one of those light lyric voices unwisely cast in a heavier role, with great vocal strain the result.

The opera succeeded almost in spite of conductor Thomas Fulton rather than for any contribution he made. "Madama Butterfly" is full of the most delicate and evocative orchestral effects. But not last night. He blanketed most singers throughout the first act. Some of Scotto's most subtle vocal effects were blurred. And Fulton made the score sound positively garish, quite an accomplishment, as it were. Repeatedly, he was out of sync with Scotto. When you have a performance like that going on in front of you, you might think that the smart thing for the conductor would be to join in.

Sets, costumes and staging are old ones, and they have lost most of their magic.

Still, except for Wagner's "Parsifal," "Butterfly" is the Met's greatest success here this year. Regrettably, it won't be repeated.