NONFICTION : TALES OF A NEW AMERICA by Robert B. Reich (Times Books: $19.95; 278 pp.).

As one whose eyes glaze over at the mere mention of a book about public policy, this one was a startling and provocative discovery. “Tales of a New America” is about precisely that: the stories Americans tell each other that define--far more than the cant Washington dishes out--the American ideal. From Horatio Alger’s morality tales to Frank Capra’s “It’s a Wonderful Life,” it is these parables, Reich suggests, “that are the unchallenged subtext of political discourse.”

Reich’s thesis is that the same core myths that underpinned our triumphant mid-century liberalism are now hopelessly out of date in dealing with “a suddenly intractable world--mostly poor, mostly non-white, in which the United States is no longer pre-eiminent.” He isolates four of those parables, which he calls: “The Mob at the Gates” (1214870636illegal immigrants); “The Triumphant Individual” (as in Lindbergh, “Rocky” or “Iacocca”); “The Benevolent Community” (Americans rolling up their sleeves to pitch in and help each other), and “The Rot at the Top” (malevolence of elites, as in Watergate). His purpose is to show how these stories no longer help us to understand either our domestic problems--such as welfare or Washington’s tangled bureaucracy--or the external threats posed by the Soviet Union or the hyperkinetic economies of Asia. Our old parables are even harmful, Reich says, reducing the debate to Manichean terms: liberalism’s feeble call for charity and conciliation on one hand, and conservatism’s aggressive insularity on the other.

Reich’s book is also timely. These same shopworn myths will undoubtedly be at the core of the 1988 presidential election.