Any tourist can go racing at the Moscow Hippodrome. It can be a pleasant afternoon with small crowds, 17 races on a program and all the cognac and caviar one could want. What takes more doing is getting to the grass roots of Russia's thoroughbred industry—visiting the country's studs. Sports Illustrated's horse racing editor is the only American journalist who has been invited to tour the breeding farms in the foothills of the Caucasus from which the Soviets hope a runner of international stature may someday emerge. The following is a diary of the trip.