Suppose you find yourself in Phoenix or Cleveland or any other of 30 most-visited American cities; here are the dining spots to seek out for distinctive food and ambience and those that are overpraised, overpriced, and overrun. Among the array of recommended eateries are those featuring every kind of foreign and regional cuisine (in Detroit, from Arabic to Soul); the top hotel dining rooms and some rustic country inns; delis, pizzerias, kosher and vegetarian restaurants; where to get the best business breakfast or lunch and the best fast repasts; where to find seclusion or all-night service. Best of all, maybe: where to eat IF YOU HAVE TIME FOR ONLY ONE MEAL. Not every city has a listing in every category, of course; the pleasure is in finding a restaurant with music on a Seattle pier, a Southern boardinghouse meal in Atlanta--plus a reminder of those legendary places (like Arthur Bryant's Barbecue in Kansas City) that just might slip the mind. The descriptions are helpful and relaxed, and for each city there's a brief culinary history. Calvin Trillin fans will lap it up but anybody bored with microwave oven dinners can benefit. Try, for instance, treating the kids to the best hot dogs in town.