FAMILY HAPPINESS <i> by Laurie Colwin (Harper & Row: $7.95)</i>

Although her short stories tend to be superficial, Laurie Colwin’s “Family Happiness” displays a richness of characterization reminiscent of 19th-Century British novels. Polly Demarest is the put-upon peacemaker in an eccentric, upper-middle-class Jewish family. When she finally tires of catering to the crotchets of her querulous relatives, she indulges herself for the first time and obtains something she really wants: an extramarital affair with the sensual painter, Lincoln Bennett. The pleasures and pains of their liaison help Polly to assert her independence and realize that her personal worth extends beyond doing what her family expects. In terms of conventional morality, she does stoop to conquer--which makes the conquest all the more delicious.