He's been called "the greatest rock guitarist in the world" The Rolling Stones once asked him to join their group And hardly anyone has ever heard of him. His name is Roy Buchanan, and he is one of the most talented - and enigmatic - figures in American music today. NET presents him to a nationwide audience for the first time in a show entitled "Introducing Roy Buchanan!" on PBS' Special of the Week. Rock impresario Bill Graham, who once ran the fabled Fillmore's East and West, will host the program, which includes a live concert from New York by Buchanan and his rock group. In a filmed portion, Buchanan displays his virtuosity in other musical genres as he performs with country-and-western stars Merle Haggard and Roy Nichols, jazz artist Mundell Lowe, and the Johnny Otis blues band. In the 16 years since Buchanan left his home in Pixley, CA, at the age of 15 and drifted eastward, his musicianship has become almost legendary in the musical underground.