That title's misleading: the portrait (in this 63-year-old New Zealand author's second novel, though first US publication) is of a marriage between two artists, and comes attached to an elaborate family chronicle. When 52-year-old Jack McAlister dies of a heart attack in l987, he's New Zealand's most respected novelist, while his wife Sarah Tandy (first seen launching Jack's last, posthumous, book) is a painter of note who's exhibited in London and Sydney. The two were childhood friends in Hawke's Bay, a bucolic community perfect for raising kids but less good for expanding minds. When Jack accidentally gets the 17-year-old Sarah pregnant (the year is 1952) and their parents reluctantly consent to their marriage, the lovebirds seize the chance to move to the big city (Wellington, the capital) and don't allow the birth of baby Dora to throw them off their creative stride. Jack does his four pages a day, while Sarah knows she must ``keep her energy for painting'' and learn from Otto Becker, a wonderfully helpful retired Austrian Jewish art teacher she's met on the beach. ``Jack understood Sarah's need to work...they shared the tunnel-vision selfishness'' of committed artists. Though the marriage will later be strained by Jack's drinking and fooling around, essentially it's a harmonious arrangement--but this lack of a core tension is bad news for the reader, who must make do with self-contained episodes (a second accidental baby, a year in London) as the novel moves through its 44-year span and a crowd of minor characters. Finally, it's prize- winning Jack who steals the show (Sarah's Sydney success getting only one paragraph). Jack and Sarah's creative struggles are obscured by domestic trivia, making this no more than a mildly agreeable read.