One of the local radio performers - a monologist, I suppose, since he neither dances, sings nor tells what are looked on commonly as jokes - is Jean Shepherd, whose appeal escapes me. Followed by a loyal clique, he appears to be a calculated surrealist of the wireless, a kind of Dali or Cocteau whose rambling non sequiturs are too arch, too precious for me to enjoy. The devil must be given his due, however, and the report is that there is a new book in the stalls, "The Night People's N.Y. Guide to New York,'" In which Shepherd has contributed some sharp, almost poignant comments on Manhattan. The book itself is the work of three out-of-towners who have come up with some absorbing information for those of us awake after dark such as where to rent a dinner jacket at 1 a.m. and how to get a dish of arroz con calamares (squid and rice, Charley) at 3 a.m. "It's a great town to live in and a great town to flee from," he says, "but once you have really tasted it, you can never forget it completely." Ah, yes. How many expatriates, voluntary and otherwise, have told me the same thing in Paris, Rome, London or Honolulu. All of us here have our advice to out-of-towners and Shepherd is no exception. "Do not expect to be welcomed to New York," he warns. "It will s1mply envelop you and will shed no tears when you leave. It is very difficult in this city to cause a ripple that lasts for more than a few moments."