It's hard to top yourself when your last baseball outing was the magical The Boys of Summer and it's certainly not a calamity if this excursion to America's playing fields--illustrious and otherwise-isn't quite as spellbinding as the saga of yesteryear's Brooklyn Dodgers. What Kahn has achieved here is a mosaic of baseball images and realities: the Astros playing at a loss in the dome that was hailed as the Eighth Wonder of the World; the grit and pride of a Double-A team of minor leaguers in Pittsfield, Mass.; the heroic memories of Artie Wilson, who remains unknown because he played out his glory years in the old Negro leagues. (""I played against Willie Mays' daddy back then."") Though Kahn keeps sentiment in decent bounds, it does seem to him that the healthiest sectors of baseball are the least visible and the least profitable. He finds his inspiration in the toiling of the Golden Eagles, a college team from Siloam Springs, Arkansas, and on the sandiots of the Puerto Rican leagues where every boy dreams of becoming the next Roberto Clemente: ""It is their national fanaticism."" But winners are not to be scorned, and a champ is a champ is a champ whether he is restaurateur Stan Musial or boat-salesman Early Wynn--or Johnny Bench for whom the last World Series was a personal triumph. Baseball fans about to tune in on the new season can warm up with Kahn's bittersweet gleanings of the summer of '76.