by ROBERT NYE 452 pages. Little, Brown. $8.95.
Sir John Falstaff, fat rogue, globe of sinful continents, candle-mine, sweet beef, whoreson round man, is not a character who requires fleshing-out. Prince Hal's drinking chum can hardly be made rounder or thirstier. Nor does he present a puzzle: his belly is his biography. Nevertheless, Robert Nye, a British poet who lives in Scotland, has had the colossal cheek to come forward with this swollen, rumbustical bladder of a book, supposedly Falstaffs bragging last confessions.
Nye's counterfeit turns out to be exactly what it should...