The New York City Ballet has such long seasons in New York that it's difficult to imagine what life would be without it. The sense of continuity it offers is matched only by a handful of other institutions. Lest one take the City Ballet's venerability for granted, however, here's a round number to make one freshly aware. The current season - they have two or more each year - at the New York State Theater through Feb. 21, is the troupe's 75th in New York since its founding in 1948. That's a lot of history under the bridge.
The opening-night program recapped that history with dramatic sweep. It began with the oldest extant ballet by George Balanchine, the City Ballet's artistic director, and concluded with two dances made last June for the Tchaikovsky Festival. Within some two hours we traveled from 1928, when Balanchine made ''Apollo,'' up to the immediate present: Jerome Robbins's ''Piano Pieces'' and Peter Martins's ''Symphony No. 1.''
One of the interesting aspects of the program was that, although we flew through the decades as though on a time machine, the language of the dances remained resolutely the same. Whether the speaker, as it were, is Balanchine, Robbins, or Martins, the permanency of the classical style holds fast. It's also elastic enough to produce ballets as dissimilar as those on opening night.
Ironically, it was the oldest ballet that looked the most modern. Perhaps this is one reason why ''Apollo'' is considered a masterpiece. Given the luminous performances it received from Peter Martins in the title role and Suzanne Farrell, Kyra Nichols, and Karin von Aroldingen as the three muses, the content of ''Apollo'' became as radically unorthodox as it must have been in 1928.
In Balanchine's conception, the god and goddesses are gently knocked from the pedestals tradition puts them on. We view them with affection and amusement. Only at the end do they become godly in the conventional sense, do we regard them with awe. Apollo moves roughly and robustly, not so much testing his strength as discovering it. Two of the muses goof when displaying the facets of their art before a rather stern Apollo.
Only Terpsichore, goddess of the dance, captures Apollo's eye with her innate grace and seemingly natural form. In so doing she instructs Apollo not only in physical mastery but in moral grace. He experiences tenderness and perhaps love in his duet with her. After a bit more rambunctious play with the muses - sport really is irresistible to this group! - Apollo finally assumes his godly place in the universe.
Time seems only to have deepened ''Apollo's'' originality of spirit. As for the other two ballets, time has played tricks. Robbins's ''Piano Pieces,'' which looked so adorable and inventive at its premiere during the Tchaikovsky Festival last June, looks at second consideration threadbare in the charm department and much thinner dancewise. A long piece, the longer it goes on the more weight it loses.
Time has sharpened the ambling nature of Martins's ''Symphony No. 1''; it knows not where it goes. But its lead dancer, Darci Kistler, knows more than ever who she is.
Still in her teens, Kistler had astounding authority right from the beginning of her career a year and a half ago. Since last June she's ripened tenfold. What will happen by February to this time-defying kid? Stay tuned in through the season.