ROBBINS'S DUAL CAREERS
``Jerome Robbins' Broadway'' encapsulates a golden age of American musical theater, as exemplified by a master artist-showman who is also a master of ballet. In returning as a choreographer to the grubby Great White Way after an absence of 25 years, Mr. Robbins demonstrates, among other things, to what extent ballet's gain was Broadway's loss. Since his triumphant Broadway exit after ``Fiddler on the Roof'' (1964), Robbins has been creating works for the New York City Ballet, where he now shares the post of co-director with Peter Martins. Robbins likes the ballet world, because it has few of the time constraints or critical and econonomic pressures of the theater, and it allows him to work quietly on his own material without the stimulating but taxing collaborations demanded for the stage.