This is Alison Lurie's fifth book -- the author who, with her debut, was called the best writer to emerge from Radcliffe since Gertrude Stein and who is now compared to Jane Austen (Elizabeth Hardwick) and Lady Herod (Gore Vidal) -- an unlikely trinity to reconcile. But certainly as a novel of all that's been going on and popping off in the '60's this could hardly be anything less than social commentary or anything more as entertainment. Miss Lurie is a writer of genuine wisdom and sophistication -- over and above that applique of chic with which a good many urban postanalysands (Kaufman, Gould and even Jong) have been diverting us and without any of the determined Savage, Symbolic Seriousness of say Piercy. The war between the Tates begins when Erica, 39 and a little out of sorts (her lovely children who were once Muffy and Jeffo have become tiresome adolescents) discovers that Brian, a liberal professor who is stiff-necked around the house, has been having an affair. With a hippie student Wendy, in leather with no fringes attached until she finds that she's pregnant. Probably Erica should have noticed earlier that Brian had changed-with his sideburns growing slowly ""like some geological formation."" Actually he hasn't -- really, but it's Erica who decides to do something about Wendy, a figure of crumpled pathos; at first she nobly flirts with the idea of adopting the baby a la E. Nesbit; then she decides Brian should marry her. There are funny, funny scenes innumerable beyond mention; with Danielle, Erica's divorced friend who belongs to a feminist rap group; with Zed, whom she once knew as Sandy, a bony and wan figure at the Krishna Bookshop who proves to be ""too nice to be a man."" And all of it takes place against the social/political/moral upheaval of an era which -- can it be -- is only five years away. But then as Danielle says, echoing the depleted way we feel now about how it was then: ""I don't care about rock festivals or black power or student revolutions or going to the moon. I feel like an exhausted time traveler. All these new developments they have, maybe they're interesting or depressing or amazing, but they have nothing to do with real life."" For all her effortless, flash fire wit, Alison Lurie never loses her perspective of what real life is all about. This could be the most indispensably attractive novel of the season.