Tonight's documentary special on the new recording last summer of Leonard Bernstein's "West Side Story" certainly had its fascination: It was the first time the composer had conducted it. Lots of passages were used that didn't appear in the original cast album in 1957. And it seemed, with such resplendent cast, a necessary step toward "West Side Story's" assuming its almost inevitable place as an important opera. (That has already happened in Europe.)

A viewing of the 1 1/2-hour program, "Bernstein Conducts 'West Side Story' " (on Channel 26 and Maryland Public Television stations at 9 p.m.), shows that there is considerably more than that.

The casting of Kiri Te Kanawa in the lead role might just have been a prima-donna exercise, though a very classy one. But just listen to what she has to say about the part in a quite moving segment, with those gorgeous brown eyes seemingly close to tears: "You know. It is the story of the young girl, and the young boy. This is the music I grew up on.

"My young man was a pianist. And we were going through the same kind of experience. And he could play this music like heaven, I thought. And we would just go around performing it all over the place. For me it played a very important part in the young love of my life.

"And now I find myself doing it with this genius. I just can't believe all that music oozed out of that mind."

Unfortunately, there is no simulcast with tonight's telecast, but on the recording that resulted from these sessions it is clear that Te Kanawa's sound could hardly be more right. Some may quibble with the accent -- it doesn't sound quite like Carol Lawrence -- but this is just one of the prices this work will have to pay for its proper passage into the opera house.

Two singers on the recording are just about perfection in every sense. Tatiana Troyanos (who grew up on the West Side) takes on Chita Rivera's Anita with all the manner and more of a voice, and Kurt Ollmann's Riff is almost ideally tough. Jose Carreras' Tony may not sound so Anglo, but, once again, that's the price you pay for opera.

In the program, "West Side Story" is referred to as "Bernstein's musical," which may be a little hard on Jerome Robbins, Arthur Laurents, Stephen Sondheim and Roger Stevens. But, let's face it, "Porgy" has become George Gershwin's opera, not DuBose Heyward's. Leonard Bernstein's conducting here brings a previously unrealized symphonic dimension to the score.