The nominal hero of this unblushingly sentimental but never mawkish memoir is a racehorse bred by the author. Barred from realizing or even testing his champion. ship potential by a freak accident, Owen (who shares Smith's middle and last names) still became some kind of winner--as a mount for handicapped children at a hippotherapy center in upstate New York. Much of the narrative is devoted to Smith's lifelong passion for horseflesh in general and Thoroughbreds in particular. An enthusiastic and knowledgeable $2 bettor, he managed to combine his avocation with gainful employment as a news-paperman. Still single, Smith left the New York Post to write books in the early 1960's, making the best-seller list his second time out of the chute with When the Cheering Stopped--a well-received study of Woodrow Wilson's last years. In addition to fame and fortune, Smith soon acquired a horse-fancying wife, Jayne. In relatively short order, the newlyweds quit Manhattan for a meadowland property in exurban Poughkeepsie, which had a 1791 Colonial, plus barns and pasturage enough to accommodate the inevitable equine influx. By Smith's gritty account, there's as much enervation as adventure in racing at the do-it-yourself level. Stable mucking, late-night feedings, veterinary bills, and related realities make the sport of kings a costly, time-consuming proposition. Only the love of Thoroughbreds themselves and the hope of breeding or buying a stakes winner keep break-even owners like the Smiths in the game. The author, for one, had great expectations for Owen Smith, whose less than classic looks were offset by a pedigree that boasts the bloodlines of Sword Dancer and Damascus. Tragically, however, the colt suffered a debilitating injury as a year, ling that not only kept him from the races but also threatened his life. Owen pulled through, though, and the disappointed Smiths found their way to the North American Riding for the Handicapped Association, which put the horse on a slower but triumphal track. The call: The Champion shows early foot, speeds down the backstretch, and closes strongly--an almost sure bet for the silver screen.