In Churchill, Manitoba, on the west coast of Hudson Bay in coldest Canada, children are shown a film each year to instruct them on civil defense, not against H-bombs but against polar bears. "Avoid a serious confrontation," the announcer in the film warns. "Stay calm and play dead . . . . Resistance would be futile."

Each year the town of Churchill sits there in the path of migrating bears who come padding through willy-nilly, and if that sounds like a slightly cute predicament, a man who lost an arm to one of the bears will tell you it's not funny. "Polar Bear Alert," tonight's National Geographic Special scheduled at 8 on channels 26, 32 and other public TV stations, is an absorbing essay on a very practical conflict between Mother Nature and her human beings.

To a hysterical woman who's just had her back door assaulted by a poky polar, the bears are The Enemy, and something should be done about them. But to scientists tracking them in a helicopter, they are fascinating exhibits to be momentarily halted with tranquilizing darts and outfitted with beep-beep radio collars so their migratory patterns can be charted. "Looks like a fatty," says a scientist to a helicopter pilot as they close in on a bear. Moments later we see him lying on his back, looking helpless and embarrassed; then he stumbles to his feet as the drug wears off and the fellows get the heck out of there.

"When the worlds of man and bear collide, most often it is the bear that loses," notes narrator Jason Robards of this seeming environmental impasse; the town can't be moved, and the bears have their date with destiny each year. Like all the Geographic specials--more than some of them, less than others--this one is filled with terrific animal photography and with good will toward man and bear. James Lipscomb wrote and directed it, and photographed it with James Deckard, and good for them.