The road from Birdy (1979) and Dad (1981) to the kind of corn Wharton lately produces isn't a happy one. The chracterizations in Seurnber (1984) and Pride (1985) and now in this Christmas-Eve heartwarmer have hinged on a weak but happy man trying to do his best for everyone concerned--and if by now it strikes some readers that Wharton is rewriting the Santa Claus fable, this book won't banish the impression. Will, an American teacher of philosophy at a Paris college, spends Christmas with his grown family in a primitive French country mill they own. This year, all the grown children are returning from the States (a teen-ager, Ben, still lives with Will and wife Lor), with various loose ends to be exhibited if not tied. Unbeknownst to the children, Will and Lor are struggling with their long marriage's greatest crisis: an affair by the wife after years of sexual apathy with Will. Will is just hoping that general goodness, trust, and history will keep the bond together, When, on Christmas morning, knitted stockings on the mantlepiece appear (no one made or stuffed them), it seems that Old Saint Nick's mysterious invervention bodes well for the family in this and other ways. As always, Wharton writes attractively, with an unpretentious stylistic lope--but the book too much resembles the ""Men"" columns of Sunday newspapers or extended Andy Rooney commentaries: cloyingly ""aw-shucks,"" admitting fault like crazy, but still a narcissistic little strategy that romanticizes emotional ham-fistedness. Forced and not credible.