After watching all 90 minutes of "An American Ism: Joe McCarthy," the anecdotal biography on Channel 26 at 9 tonight, one may feel like the dissatisfied newsreel editor at the beginning of "Citizen Kane." Yes, yes, it's all very nice-but something is missing.

Producer-director Glenn Silber, who made the documentary for the Wisconsin Educational Television Network, interviewed those who knew McCarthy as a young chicken farmer and rising politician in his native state as well as some of those he victimized during the incendiary Communist witch-hunts of his Washington career. They do shed a peep or two of new light on the man who rose to become the most infamous domestic menace of the American '50s; in essence, this is a monster movie starring the survivors.

The beast, however, did not arrive from another planet or crawl out of a nuclear test site. He emerged from a political context, and the film doesn't supply any more of that than previous works on McCarthy have; it may in fact provide less. Of course, the only way to "explain" McCarthy and how he grew may be to go back and interview the entire nation as it was during the first frosty mornings of the old Cold War.

"An American Ism" doesn't say a great deal more about the adult McCarthy than did NCB's failed but dead-earnest "Tail Gunner Joe" or Emile de Antonio's spine-tingling documentary on the Army-McCarthy hearings, "Point of Order." De Antonio is credited as a consultant to Silber and the man whose "idea" inspired the project, a contribution that smacks of at least tickling if not beating a dead horse.

The most piquant observations are from those who knew McCarthy early. "He was a hick," an old neighbor recalls, "a target we liked to tease" as a child because he was "awkward-looking" and "always doing the wrong thing." This awkwardness, commentator Jack Anderson says, much, much later, was turned into an asset during McCarthy's table-thumping and finger-pointing Capitol Hill extravaganzas.

McCarthy brought to politics and the mass media "a different kind of demagoguery," says Anderson, bumbling fashion that made him appear to be sincere. He was a disarming demagogue."

Unfortunately, Silber deploys the resources of the documentary film-maker-old photos, headlines, newsreel footage, interviews-with an awkwardness that is not an asset. His philosophy seems to have been, "If you have an old picture, show it," and the program is an attic full of visual clutter from beginning to end. Nevertheless, as a collection of revealing or at least diverting footnotes, "An American Ism" comes across as valuable, authoritative and, considering the volatility that still surrounds its subject, commendably dispassionate.