One of the most imaginative raconteurs in the history of broadcasting is Jean Shepherd, who is heard Monday through Friday nights and on Saturday afternoons on WOR radio. Mr Shepherd has been reminiscing, musing and expressing opinions on a broad spectrum of subjects over the same station for years. But he shows no signs of running out of subject matter. He is often brilliant, sometimes a trifle mad, and generally well worth hearing. On Saturday afternoon, he provided his listeners with a vivid description of a boyhood encounter with a fighting dogfish at a lake in Michigan. On other occasions he has held forth caustically on status seekers., advertising techniques, movie-promotion stunds and vice in the Army. He has also talked about some of the old radio shows. When he recalled "Jack Armstrong - the All American Boy," he sang with vigor that program's theme song, "Wave the Flag for Hudson High, Boys." It was a reminder of a piece of nonsense that, with the passage of years and with the help of Mr. Shepherd, somehow took on nostalgic aspects. Mr. Shepherd's criticism about sponsors and commercials is ironically belied in some of the lengthy announcements that he delivers on behalf of his own advertisers. A les gifted storyteller would probably lose most of his audience during these intervals. One suspects, however, that the Shepherd follower suffers through the blurbs in hope of hearing better things when they are over. It is inconceivable that Mr. Shepherd could ever work successfully from a formal script. His flights of fancy must be the spontaneous products of an agile and unfettered mind. He has also been seen on television and in several stage productions, including the current revival of "The Tender Trap" at the 41st Street Theatre. But the radio is his real home.He has an uncommon ability to create images and to transmit them to his audience in delightful style.