As a strong, silent type on the movie screen and, more important, the author of plays that are loud eruptions of anguished language, Sam Shepard has long been an odd, contradictory presence on the American cultural scene. He's well-known but unknown, handsome and seductive but willfully remote. He's almost too easily the archetype of the authentic American, at home in the wide open spaces but not really at home anywhere.

He's also notoriously publicity-shy, which is primarily what makes ''Sam Shepard: Stalking Himself,'' on PBS tonight at 9, such a surprising viewing experience. In addition to snippets of Shepard's emotionally grueling plays and interviews with the actors who have lovingly interpreted them, this hourlong program includes a close conversation with Mr. Shephard. And in his abashed, semaphoric way, he gives an eloquent account of where he comes from and what he's about as a relentlessly creative person.

It's an appropriately colorful tale, which is effectively illustrated with a melange of old photographs and filmed vistas, giving ''Stalking Himself'' the feel of a social document as well as a personal one. At 18, Mr. Shepard had just left a troubled home in the desert town of Duarte, Calif., and was working as a newspaper deliveryman in Pasadena when he spotted an ad for a traveling theatrical company. He signed on, hopped on a bus and discovered what he describes as the ''mobility of theater,'' a life force that soon landed him in New York City, right in the middle of the Off Off Broadway explosion that was happening at places like Theater Genesis at St. Marks Church in the Bowery.

By night, Mr. Shepard worked as a busboy at the Village Gate, where he had a rare view of such jazz geniuses as Thelonious Monk and Nina Simone. By day, he started to write orphic, absurdist plays that no one seemed to understand but that almost immediately won him the acclaim and support that would continue as he moved on to London and to the world of movies.

Throughout his account, Mr. Shepard offers moving if spare reflections on his times. ''Well, for me, there was nothing fun about the 60's,'' he says, with a conflicted look in his eyes that tells even more. But his words are most moving when he is talking about the point in the late 70's when he realized he needed to write drama about his traumatic childhood, especially his relationship with his haunted father. ''I didn't really want to tiptoe in there,'' he says. ''But I figured I'd better.''

He did, of course, and what resulted were his best creations, plays of the 1980's like ''True West,'' ''Fool for Love'' and ''A Lie of the Mind.'' (At 10, PBS is rebroadcasting the 1984 ''Great Performances'' version of ''True West,'' starring John Malkovich and Gary Sinise, proof of Mr. Shepard's accomplishment.)

''Stalking Himself'' includes occasional revelations about Mr. Shepard's private life. It's rather stunning to learn, for example, that this man who won an Oscar nomination for his portrayal of the ace pilot Chuck Yeager in ''The Right Stuff'' has refused to fly in airplanes for many years. But the program is really about Mr. Shepard and his work, and what it reveals most assuredly is that he really is the authentic American artist, always traveling in the direction that he alone chooses.

As Edward Albee, a playwright Mr. Shepard admires and has much in common with, puts it: ''Sam was always taking chances, always being original. Somebody who was willing to fail and fail interestingly. And if you're willing to fail interestingly, you tend to succeed interestingly.''