by Anthony Burgess.Little, Brown, $4.95. Mr. Burgess imagines that John Keats met, and influenced, the Roman poet Giuseppe Belli, and describes how that could have happened. The novella about the doomed and resentful Keats is poignantly convincing. The appended translations from Belli (also by Mr. Burgess, although he chooses to pretend otherwise) produce a curious effect. Their content is antitheological and, because there is simply no English equivalent for Belli’s Roman street argot, their style suggests Byron trying, with no great success, to talk Cockney.