When pressed for a history of the American '40's, author and Harper's Magazine editor Allen ruefully referred to himself as a ""ten year locust"" -- his Only Yesterday (the '20's) and Since Yesterday (the '30's) offered Americans best-sellers (one million copies sold of Only Yesterday) which dealt with the significance of attitudes and events within their own recent past. Although Allen considered himself a ""pseudo-historian,"" Only Yesterday, Payne feels, provides ""a prevailing image of the post W.W. I period"" for some time to come, since Allen's political stance was ""liberal"" before that word became a synonym for articulate inaction. ""I'm afraid I'm one of those damned liberals . . . protesting against the established order and wanting justice for the underdog. . . and ready if (he) got in power to shift around and protest on the other side."" As magazine editor-in-chief he was careful never to impose his own outlook; Allen sought primarily ""the seminal idea. . . the new perspective"" not tied to any publication ""image"" or advertising/mass readership pressure. Payne traces Allen's life from New England roots, Groton, Harvard, government and Harvard PR posts through the prolific years of writing and editing; his two happy marriages and two personal tragedies, his travels, friendships with authors and literati, and a diversity of pleasures. But the vitality of Allen's life and his scrupulous attention to the skills and raison of his trade are evident in his formal and informal prose -- from which Payne has made selections with taste and relevance. A modest and decently critical estimate of one of the last of the gentlemen editors who illuminated for a good number of us a few of our yesterdays.