by LYNN CAINE
223 pages. Morrow. $6.95.
Lynn Caine has a bit of the style of the only decent character in a Lois Gould novel. Until five years ago, she and her husband Martin lived comfortably in a Central Park West apartment, making the adjectives "happy" and "hectic" synonymous as only New Yorkers can. Attractive and fortyish, she was (and is) a publicity manager for Little, Brown. He was a successful lawyer, specializing in bankruptcy. They loved their two children, aged four and eight, Mozart, fine wine and summer vacations in New England....