Using important music (Gershwin's Piano Concerto in F) and sleekly modern decor by Santo Loquasto, Jerome Robbins has just created an exceedingly trivial ballet for the City Ballet. ''The Gershwin Concerto'' is all manner and no substance. The large ensemble stands around looking sultry, waiting, as it were, for Robbins to get an idea.
He gets one: social dancing. So everyone Charlestons for a bit, and then it's back to posing around the stage. One possibly viable idea is the contrast Robbins sets up between his leading women - the austere Maria Calegari and the perky Darci Kistler. But their personalities seemed dubbed to the music rather than a natural emanation of it.