Nonfiction briefly . . .; Fading Feast: A Compendium of American Regional Foods, by Raymond Sokolov. New York: Farrar, Straus & Giroux. 276 pp. $17.95.

The urbanization of America has meant the standardization of its eating habits. Many regional foods -- from New England gooseberries to Northwest Coast ''Olympia'' oysters -- have fallen through the cracks of our mass-food-delivery system. Only a few country-kitchen survivors still remember how to serve up the local fare.

This unappetizing situation moved Raymond Sokolov to act. ''As the roving food columnist for Natural History magazine,'' he writes, ''I talked with these last, authentic exponents of regional foods, learning their recipes and recording the food wisdom of our past before it fades completely from view except at pumped-up special events.'' His two-year mission took him to Gnaw Bone , Ind., in search of wild-persimmon pudding; to Louisiana for Cajun blood sausage; to Florida for real Key lime pie; to Arizona for Hopi blue cornbread.

Although there are recipes here, to be sure, Sokolov's focus is much more on the local cooks who prepare them, on the origins of the foods they use, and on his own experiences in tracking them down. He explains why Michigan's Finnish-Americans eat Cornish meat pasties, and why it is illegal for sports divers in California to possess more than four abalones at a time. ''Fading Feast'' is a literary tossed salad -- part travelogue, social history, and cookbook, enhanced by a graceful, unlabored style and topped off with 15 color photographs. Spencer Punnett