The Spoleto Festival's new production of "Madame Butterfly" ends with the atom bomb exploding over Nagasaki, a bit of demolition that climaxes an explosive new interpretation of Puccini's sentimental classic. Its first performance, Friday night, opened the 2 1/2-week festival of theater, opera, chamber music, dance and miscellaneous street entertainment.

"I read through the libretto and listened to a recording," says British director Ken Russell, who is best-known for his film work ("Tommy" and "Altered States" are among his dozen credits in this medium). "As soon as I noticed that it all happened in Nagasaki, that was it. I had my concept--in a flash, as they say."

The atomic explosion is not a part of the plot, but an editorial comment. The Hiroshima and Nagasaki explosions, Russell believes, are a logical consequence of the American attitudes embodied in Lt. B.F. Pinkerton: his ignorant condescension to the ancient, complex culture of Japan and his callous abandonment of his bride.

On stage, the bomb drops during the orchestral postlude after Cio-Cio-San has stabbed herself to death with her father's dagger. While the music is telling the audience that the tragedy has ended, the stage picture takes two quick leaps in history--first to the A-bomb and then to the present. "I hope he Russell will not blow us all up with his atomic explosion," the festival's founder and artistic director, Gian Carlo Menotti, said apprehensively before the opening night. His fears were groundless; it was a mild, noiseless, indoor sort of atomic explosion, and the audience survived. But "Madame Butterfly" may never be the same again. Russell Clips Butterfly's Wings

In Russell's conception, the opera happens in the late 1930s, not long before Pearl Harbor. Cio-Cio-San is a prostitute who sees her marriage to Pinkerton as a way to escape from her degrading life and into the American dream. Unlike the nuclear explosion (which was beyond the dreams of Puccini and his librettists), at least part of this (the escapist part) is implicit in the libretto. There is nothing there about prostitution--Butterfly is a geisha, a very different sort of profession. Russell believes (not without justification) that the libretto misinterprets Japanese culture; a marriage between a geisha and an American sailor would be unthinkable, since contact between geishas and foreigners was almost unheard of, but a marriage between a sailor and a prostitute could have happened.

In any case, Cio-Cio-San certainly does want to abandon Japanese culture and become an American. This is made clear, to some extent, in all productions of "Butterfly," with discreet use of an American flag, a chair (totally alien to Japanese traditions of home furnishing) and sometimes a collection of Christian pictures and statues in the decor of Butterfly's home after she becomes "Madama B.F. Pinkerton." Russell, however, sharply escalates the motif.

Besides an enormous American flag, he puts a painting on one wall, Japanese in style but American in sentiment: the head of Abraham Lincoln encircled by the words "In God We Trust." Another wall is decorated with a large, cutout head of Mickey Mouse, and the room is dominated by an enormous American refrigerator--an old-fashioned one, with the motor mounted on top. After her husband has loved her and left her, Butterfly does not return to the oldest profession. When Goro (who is a pimp and con man, not a marriage broker) brings her a new client--Yamadori, who is dressed as a Japanese naval officer--she rejects him scornfully.

She is supported by the earnings of her friend Suzuki, not really a servant as in most productions, but a fellow prostitute. There are very slight hints of a possible lesbian relationship between Butterfly and Suzuki, but this is not stressed. Butterfly sits around her "American" apartment dreaming of her life in that strange, big country to which Pinkerton will take her "when the robins build their nests again." She dreams and smokes opium--to which she had introduced Pinkerton on their wedding night. Il Yankee Vagabondo

Perhaps the opium explains why Pinkerton's music was so romantically ardent at the end of Act I. Earlier, he had been extremely cynical, treating his "wedding" to Butterfly as a sort of joke and dallying with a prostitute even as the wedding procession drew near. In his first big aria, he describes himself as "Il Yankee vagabondo": "Wherever in the world the footloose Yankee goes, he looks for enjoyment and profits. Scorning risks, he drops anchor at random . . . His life does not satisfy him unless he can make his own the flowers of every shore and the love of all the fair ones."

In most productions of "Butterfly," the dark side of this statement is glossed over; it all sounds so pretty in Italian with Puccini's rollicking music. But the dark side is there, and Russell's direction makes the audience acutely aware of it. Puccini gives Pinkerton a lot of cynicism, and the whole opera is rich in anti-American sentiment--notably in the parodistic use of "The Star-Spangled Banner" as a drinking song (which the tune was, originally) and as a general leitmotif in various fragments and distortions. In Act II, when Cio-Cio-San brings out her son to show him to the American consul, Sharpless, the orchestra comments on the child's mixed heritage by mingling a bit of "The Star-Spangled Banner" with a Japanese melody. In the Spoleto production, conductor John Matheson underlines this point more clearly than any other conductor I have ever heard in this opera. He is echoing faithfully what Russell has done with the staging. Culture Shock and The American Dream

"Madame Butterfly" has always been an opera about culture shock, no matter how much this aspect was played down in some productions. Russell stresses it from the beginning. Those who are accustomed to "Butterflies" with lots of bamboo, cherry blossoms and kimonos will be shocked as soon as the curtain rises. The set is not the usual quaint Japanese home in the country ("the chicken coop on the hill," as Russell described it in a conversation.) It is a three-story building with Butterfly's apartment on the first floor, a very busy brothel on the second, and lots of street action on the perimeter--including vendors, prostitutes picking up tricks and an old man smoking opium more or less continuously. There are practically no kimonos; Butterfly wears one for her wedding, but most of the guests are fellow prostitutes in Western garb or sailors who come in carrying cases of Coke and Pepsi. Goro, who seems to be running a sort of protection racket among the street vendors, wears a double-breasted suit and a bow tie.

Russell's interpretation may be summarized as 2 1/2 hours on the Americanization of Japan followed by a quick flash of the atomic bomb and then a few seconds on the Japanization of America. As the curtain falls, the stage is filled with Japanese logos that have become familiar here: Sony, Honda, Datsun, Casio, Suzuki, Mitsubishi Car Audio--hanging in midair as though they are fallout from the Nagasaki explosion, surrounding and engulfing a lonely Coca-Cola logo. Perhaps he is trying to tell us that we have awakened a sleeping giant.

The American dream, Butterfly-style, is most vividly embodied in a wordless pantomime sequence that ends Act II, during the postlude and humming chorus. In her opium dream, Butterfly is in America--a home decorated essentially like her apartment, except that it is dinner time. There is an enormous hamburger (three or four feet in diameter) and a colossal package of Kellogg's Corn Flakes, from which she strews flakes on the floor, just as she was strewing flower petals a few minutes ago in real life. A monster catsup bottle and a truly giant can of Green Giant peas complete the decor. Pinkerton comes home from work and she seats him at the table with his evening paper and his opium pipe.

All this may sound like Ken Russell's pipe dream, and it certainly includes serious distortions and exaggerations. But a remarkable amount of it (perhaps 80 percent) is present or implicit in Puccini's work and has been simply glossed over by generations of performance tradition in a sugar-sweet, picture-postcard style. Those who have never seen another "Butterfly" might pick up some misapprehensions from this production--but a lot of what Russell has done is a simple correction of superficial practices and attitudes that have become fixed in cement since the original production. Russell's version has much more depth and strength than Puccini's work usually receives in performance. If Russell has swung too far in the opposite direction, that is the way a pendulum usually swings. And There Was Music

In the attention given to the director, it is easy to overlook some fine musicianship in this production--not only by conductor Matheson but by the Westminster Choir, the Spoleto Festival Orchestra and a well-chosen cast. The most striking performances were in secondary roles: Kumiko Yoshii as a rich-voiced Suzuki and Steven Cole, a fine tenor and a superb actor in the role of Goro, which is made even more slimy than usual in this production. Robert Galbraith did well vocally and dramatically with the thankless role of Sharpless, and Barry McCauley gave a credible, well-nuanced interpretation of Pinkerton, significantly different from those one usually sees.

In the title role, Catherine Lamy was always believable dramatically. There was nothing especially Japanese about her Butterfly, in appearance or gestures, but she was portraying a woman who wanted to become American. Vocally, she had some trouble in her upper register--thinness of tone and slight imprecisions of pitch--while she was warming up. These were more or less eliminated later, but not soon enough to avoid small problems in "Un bel di" in Act II.

This is by no means a "Butterfly" to satisfy all tastes, or even a majority. But it is carefully thought-out, provocative, well-staged and sung. We will probably never see another one quite like it, but it should have some influence on the way directors think about this opera in the future.

It will be repeated Wednesday, Friday and Sunday.