EAST SIDE, WEST SIDE (376 pp.]Marcia DavenportScribner ($3).
Marcia Davenport lived through some straitened days on New York's upper West Side, but she graduated to better things when her mother (Alma Gluck) became famous as a singer. Author Davenport now lives in the high-rent East 70s and is the author of such best-sellers as The Valley of Decision and Of Lena Geyer. East Side, West Side is a glimpse at these two worlds. It straddles Manhattan in the manner of a crosstown bus, picking up a sampling of the city's polyglot population and giving them a good shaking-up as it goes along....