THE LAST ITALIAN: Portrait of a People by William Murray (Prentice Hall Press: $19.95; 254 pp.) On a recent visit to a new Chinese restaurant in Rome, New Yorker staff writer William Murray asks his waiter--an Italian man dressed in a mandarin costume with a little round hat--about an item on the menu. "How do I know?" he replies aghast. "You don't think I eat this stuff?" It's one of many examples in this mellowed travelogue of Italy's traditional resistance to change. If Murray's portrait is a bit quixotic--the modern cities on which he focuses do indeed mark a change from the sleepy culture still found in some southern villages--his writing is evocative enough to make up for the occasional distortion.