Leonard Bernstein's "West Side Story" has always been a curiously amphibious piece of work -- popular in its subject-matter and some of its many styles, classical in its level of craftsmanship and aspirations to universal significance. Its popularity has been established through nearly 30 years of enormous ticket sales.

Its classical dimensions are now fully explored for the first time in a Deutsche Grammophon recording conducted by the composer, with a cast that includes Kiri Te Kanawa and Jose' Carreras in the leading roles, and Tatiana Troyanos and Marilyn Horne in supporting parts.

Conducting this work for the first time on or off records, Bernstein handles the score with meticulous, loving care and the music reaches an unprecedented depth and richness. For some time, as Bernstein's career advanced and his productivity dwindled, the suspicion has grown that this unpretentious Broadway show may live on as his masterpiece after the "Jeremiah" Symphony, "Kaddish," "The Age of Anxiety" and "Candide" have become historic curiosities and "A Quiet Place" has been totally forgotten. This recording confirms the impression; "West Side Story" is a classic.

Its plot is timeless, though the details are rooted in the Manhattan of the mid-1950s. The characters, emotions and symbolic overtones are taken directly from Shakespeare's most lyrical tragedy, "Romeo and Juliet." Among those who have treated this material musically -- a list that includes Berlioz, Gounod, Tchaikovsky and Prokofiev -- Bernstein has earned himself a lasting place of honor.

Musically, "West Side Story" uses virtually all of the pop styles that were current when it was composed, including Latin American dance rhythms and jazz syncopations and harmonies. But it is classical in the richness of its orchestration and in the depth and polish of its climactic arias.

This music does not have to be sung by classically trained voices -- a movie sound track and countless stage productions have demonstrated that. But it can be handled by such voices, and when it is, it rises into a new musical dimension. This does not always happen when classical performers take up popular music, as can be heard in the pop recordings of Luciano Pavarotti, Placido Domingo and countless other opera singers who have gone musically slumming. Sometimes it works, but a good many pop songs simply reveal their limitations when exposed to a classical voice's wider range of pitch, dynamics and expressive resources. Whether he did it deliberately or not, Bernstein left room for interpretive growth in a substantial part of this score.

"I Feel Pretty" belongs in the same category with "Je suis Titania," and the fact becomes immediately evident when you hear it sung by Kiri Te Kanawa. Structurally, "Maria" is a popular ballad, but when it is sung by Carreras, it becomes a cousin to the "Flower Song" from "Carmen," which was also, in its time, an amphibious piece of musical theater.

Not all of the music has classical stature; much of it is good but good in a different way. "Gee, Officer Krupke," sung by operatic voices, simply would not work and in this recording it is wisely given to Broadway voices.

Anita's role occupies the borderline between classical and popular styles, and it was an inspired decision to give it to Troyanos, an international star who grew up on the West Side of Manhattan. She is superbly demotic in "America," but builds to operatic stature in the duet, "A Boy Like That." Marilyn Horne, who also grew up with American pop musical styles, gives a classic performance of "Somewhere." After hearing her treatment, one wonders whether it should ever be done any other way.

As one listens to the production as a whole, it becomes apparent that the varied musical styles are tailored to the dramatis personae. Tony and Maria, by their love in a hate-ridden environment, are raised to a level of existence separate from the other people in the story. The fact is underlined neatly in "I Feel Pretty," where the point of the number is precisely Maria's contrast with her friends.

The music functions on two levels: operatic in the solo, pop in the chorus. In this musical subtlety, Bernstein is faithful to his Shakespearean source material; Romeo and Juliet, because they are in love, are raised to an order of being different from and superior to Tybalt, Mercutio and the Nurse.

In this recording, the soprano, who should have a Spanish accent, is a native English speaker, while the tenor, who should not have a Spanish accent, does. Anyone who has an ear for great singing will not be bothered by this. But it is worth noting that Bernstein, smashing through musical barriers in a way that he was uniquely qualified to do, chose to do it in a work that deals with the crossing of social and ethnic barriers. In the plot of "West Side Story," the effort is a tragic failure. In the music, as this recording demonstrates, it is a dazling success.

When it was new -- and particularly when it was made into a film -- "West Side Story" also broke another barrier, that of audiences. To the younger generation of that period, the Broadway musical was a genre hardly less exotic than opera itself; then, suddenly, they had a show that dealt with people like themselves, problems like their own and musical idioms that were familiar to them. A few other productions ("Bye Bye Birdie," "Hair," "Jesus Christ Superstar") managed to explore similar territory, but now it seems closed as a result of rising production costs and ticket prices -- perhaps also as a result of the change (dare one say "decline"?) in popular music styles. Meanwhile, the generation that was young when "West Side Story" was new has grown to an age where many of its members are fans of classical music. It is good to see that at least one show from their youth has made the trip with them.

This recording reached the best-seller lists, classical and popular, almost as soon as it became available -- and, for once, those lists reflect the quality of the material listed. This is one of the most notable recordings of 1985, and DG has given it the kind of lavish treatment it deserves.

The compact disc edition (DG 415 253-2, two CDs with libretto) has not one but two booklets: a libretto in English, German and French, and a set of program notes in these languages plus Italian. The digital sound is superb and presents, at last, the full impact of the splendid orchestration. It is also effective in the suite from "On the Waterfront," issued on LP several years ago, which is a bonus in the compact disc edition only. The music (which sometimes sounds like a tribute to Aaron Copland) fits well with "West Side Story," both in atmosphere and in the level of its technical skill.