"The Movie at the End of the World" is the video equivalent of home-canned vegetables: The container may be dismaying, but the flavor is marvelous. The rough-edged one-hour documentary (tonight on Channel 26 at 10:30) follows poet Tom McGrath, author of dozens of books and 20 movie scripts (including "To Fly," shown at the Air and Space Museum), as he rambles across his native North Dakota and the hyperborean plains of Minnesota where he now lives.

The region has bred many an ice-belt crank and prairie Homer, and the craggy, denimed McGrath, with his weathered face and rawhide voice, is a little of each. At a clattering fair of antique farm machinery, he inveighs against national amnesia: "We seem to be a people who forget their history every 15 minutes."

Walking through a factory, he offers neo-Wobbly sentiments: "Work is either play or slavery" (but "writing is being enslaved to play"). At the lectern, he reads from poems nostalgic for fresh-baked bread and heartland heritage; and at home he reflects on a half-century as a farm worker, labor organizer, war protester and writer. Customary docu-fare for poets.

But as the guitar music plunks along and the scenes segue heavily into each other, McGrath proves slyly humorous and wonderfully free of sanctimony. He reads a poem--"All night long I heard the owls/ Pushing their heavy lumber through the dark/They are building another room on the night"--and asks, "Get it?" We don't. "Well," says McGrath, "I don't understand it myself." And he can be hilariously hard on his own trade. One of his films, a satire on poetry readings, depicts a pompous bard who rants: "I guess all I'm trying to say is/I saw Crazy Horse die for a split-level swimming pool/ In a tree house owned by a Pawnee Warner Brothers psychiatrist!"

The Minnesota producers occasionally threaten to smother the show in gratuitous Vietnam clips and overreaching graphic effects, but McGrath's charm is finally irresistible--tough as an old stump, pleasant as the plains.