NEW YORK (AP) _ The corps de ballet, shining like eight new pennies, in perfect step and even breathing together, really was the star of ''Concerto Barocco,'' the 1941 ballet which opened the New York City Ballet's season.

The season, settling in with one of George Balanchine's trademark neoclassic, plotless ballets, began Tuesday and will continue through June 28 at the New York State Theater.

The soloists, of course, also contributed mightily - the crisp Judith Fugate, Heather Watts and Otto Neubert. The music for ''Concerto Barocco'' is Bach's ''Double Violin Concerto in D Minor.''

Robert La Fosse had danced through ''Prodigal Son'' with the company before, but now he has mastered it as dance drama. His high jumps toward his father's gate set an early tone of excitement, as they should. He beats his thighs with his fists in an adolescent tantrum.

La Fosse is taken in by drinking companions and the siren of the city; he later becomes their victim in torture. When La Fosse is injured and penitent, he is really pathetic and one feels sympathy.

''Prodigal Son,'' which Balanchine choreographed in 1929 to Prokofiev music, is a masterpiece. But it is only meaningful in this kind of performance.

Darci Kistler danced the siren's steps. Adding the necessary personality and coarseness undoubtedly are in her future.

The evening ended with Jerome Robbins' 1953 light-as-air ''Fanfare,'' danced to Britten's ''The Young Person's Guide to the Orchestra.'' Except for the three men dancing percussion, La Fosse, Jean-Pierre Frohlick and Kipling Houston, the dancers are stars-to-be. It was a good chance to choose dancers to watch in future.

One of the four horns, Jerome Kipper, was dancing his debut. He's one of five dancers entering the corps de ballet from the School of American Ballet since the company's last season.

Robert Irving conducted for the evening, which ended with a lovely fugue. It isn't every day a happy ''Fanfare'' closes a program or one sees a fugue danced.