MANHATTAN, WHEN I WAS YOUNG Mary Cantwell, who has been a writer and editor at Mademoiselle and Vogue and a writer at the New York Times, gives us an elegant and lyrical autobiographical account of a time and place that for some exists only in imagination. But this is a life as it was actually lived, with romance, passion, and no little share of pain. Like her earlier, warmly received American Girl: Scenes from a Small-Town Childhood, Cantwell's new book "offers many of the pleas-ures more usually associated with the novel" (Washington Post Book World). In five different apartments in Manhattan, each with its own character and charm, Cantwell's story winds through its phases, from single working girl to young wife and mother, from career choices and divorce to rediscovery. The world Cantwell inhabits - that of magazine and book publishing and fashion and the middle-class bohemia of downtown New York at a golden moment in time - is brought beautifully to life in a memoir that is sure to win her new readers and ren