Intelligent TV is its own reward. It may not leave you shattered or knock you out of your chair laughing, but it stays with you in ways that junk watching never does.

"Keeping On" is a low-key 90-minute drama about unionizing a small southern mill town--and that's no exaggeration: The whole town is affected, not only the textile workers.

Directed by Barbara Kopple, of Oscar-winning "Harlan County, U.S.A.," and written by Horton Foote, also an Academy Award winner for his screenplay of "To Kill a Mockingbird," this is an American Playhouse feature. It airs over channels 26 and 32 tonight at 9.

It looks real, all right. It was shot mostly in Huntsville, Ala., an unloved-looking town. The trees are bare, the streets vacant and cold. People wear coats and sweaters. The factory itself, actually a mill in Elizabeth, N.J., is grimy and dark and noisy, the workers' homes cramped. You can smell the poverty.

Until the actors start in on the expository dialogue, you could mistake it for a documentary, which of course is Kopple's background. It must be such a relief to a documentary filmmaker to be able to capture those crucial little scenes that just weren't filmable in real life, the things you couldn't re-enact.

The foreman fires a worker in a quick, nasty exchange, so quick that you--and the worker--need a second to realize what happened. The worker, appealing to the manager, is brushed aside ("Goodbye, Mr. Traylor") so easily that you understand everything about this town and its situation from that one abortive encounter.

The acting is quietly competent: James Broderick as the organizer, Dick Anthony Williams as the fired worker and Rosalind Cash as his wife, Carol Kane as a timid worker with five children. They and the others get across the feelings of the struggling poor, fearful for their jobs, wary of trusting the organizer, uneasy when the company tries subtly to play on the racism that lies beneath the surface.

The treatment of relations between the races feels accurate, most of it unspoken: such a relief from the usual TV and movie hysteria about southern small towns.

If anything, "Keeping On" is actually too low-key, too gray and subdued--from the minimal score, which consists mainly of someone whistling, to the despairing monotones of the voices. The picture never lets up. There is no scrap of humor, no laughter. The characters manage maybe four smiles in the whole 90 minutes, but the viewers get none. The classic union saga unfolds: blacklisting, brown lung, harassment, broken promises by the union hierarchy, legal delays.

And it would have been useful to see even a little of the other side. As it stands, management remains an invisible, mysterious, all-powerful monster. Perhaps the director felt that if it were demystified she would be left with another even-handed documentary without dramatic tension. Certainly she needed all the drama she could get, especially at the end, which is just like a documentary: a flurry of scenes telling of offscreen actions that change everything. One half-expects a post-credits screen crawl telling us how it all came out.

But after it is finished, for all its faults, the picture sticks in the mind: those drab people rising to an occasion, quietly, without heroics, in their different styles--the way it happens.