* Meet Lila Beneker. You probably have in some affluent suburb any number of times. She lives in Northern Westchester which she occasionally thinks of as Cheever country and she's exceptionally unexceptional and particularly disarming. This is her split level, examined life as she now has reached the point where she's having more but enjoying it less. Her son Tommy is at Harvard via summers in Mississippi; her daughter Norah has just had a baby via natural childbirth and an obstetrician who sees himself ""as the lead in Genesis""; and Mr. Beneker is wistfully eyeing a girl in a summer dress via Mary Quant. Gentle, conciliatory, confused Mrs. Beneker is trying to assimilate Great Thoughts from her General Studies course in religion; sometimes she dreams of devoting herself to Good Works although all she's been given to do so far is an afternoon of reading to a woman in a home for the aged. And in between, her very motile mind wanders charmingly, from her marketing list to her fears, her ""ferocious unconscious,"" her inadequacies when a mother's kisses won't make anything well any more.... Mrs. Beneker--well she's a more modish McGinley--and she's supremely appealing. Take her she's yours, and she could easily be everybody's.