Letter-writing has returned with a bang. A few months ago brought John Updike's first epistolary novel (53; now we have a lowbrow, beer-spray, polka-beat alternative, a screwball--er, knuckleball--exchange of letters between major-league pitchers Joe and Phil Niekro. Not that the Niekros don't have dazzling trophies to show their fans--they share 51 years in the sport, and the major-league record for career wins by brothers. They make the best of their achievements: the hunt for the record-breaking 530th victory occupies much of the book--there's even some suspense here--although the bros can't understand why their fraternal triumph doesn't catch the headlines like Pete Rose's run at Ty Cobb (""Maybe we're not flashy like Rose,"" one of them pines). The heart of the book lies, of course, in their inside account of last year's fabulous ""Scuff Scandal""--wherein Joe was found doctoring the ball with an emery board--handled with equal portions of wide-eyed innocence and sardonic humor (""I hope Mom and Dad won't think l really was cheating,"" gulps Joe; Phil responds by proposing a line of "" 'Scuffing in the USA' t-shirts and Joe Niekro power-sanders""). For filler between these two momentous events, the bros cover George Steinbrenner (""If you lose a game. . .he crushes you like you're an ant and he's a size-17 shoe""), drug scandals, the collapse of the Cleveland Indians, the difficulty of pitching the knuckleball, Phil's last game in the Majors, Joe's battle with baldness, the quest for the perfect polka joint, and other baseballiana. A perfectly silly book, but hilarious in its own way, and what more can you ask from two brothers who address one another as ""Knucksie"" or ""Knucks""?