LUCY CROWN (339 pp.)Irwin Shaw Random House ($3.95).
Lucy Crown keeps one in suspense at the end of every chapter. Will suburban housewife Lucy's summer indiscretion with a younger man turn her marriage to Oliver Crown into a lasting winter of discontent? Can the couple's 13-year-old son Tony grow into a healthy, normal American boy after he peeps through the cottage blinds and sees his mother in the arms and bed of his 20-year-old counselor-companion Jeff? Is humorless, self-contained Oliver to blame for it all be cause he treats his Hartford, Conn, printing plant as a religion and his wife as...