When somebody pounds at your door in Churchill, Manitoba, Canada, better not open it without checking on your uninvited caller. It might be a polar bear.
The National Geographic's ''Polar Bear Alert'' (PBS, Wednesday, 8-9 p.m.) is a playful hour of fun and frolic with polar bears. These bears are now protected by international conservation agreements, and so they make their midnight surprise visits with impunity.
Filmed with skill and daring (one wonders what protected the cinematographer who photographed still-photographer David Hiser snapping pictures of polar bears from inside a wire cage), ''Polar Bear Alert'' is cute but not ''cutesy.'' Thank goodness there are no scenes of bears moving to the beat of the ''1812 Overture.''
The program was written and directed by James Lipscomb, hosted by E.G. Marshall, and narrated by Jason Robards, a playful creature with a hard wallop himself, just like the polar bear. It is meant to entertain as it educates -- and you will find yourself a student of polar bear sociology, psychology, and perhaps even philosophy. Polar bear philosophy seems to be: live and let live while playing hard.
Just about everybody in Churchill, a town on the west coast of Hudson Bay in arctic Canada, feels ambivalent toward the white creatures, which have been known to maul citizens even as they forage in their garbage. The natives have learned to live with the bears, although there is still fear and wariness of these unpredictably fierce creatures.
On Halloween night in Churchill, nervous authorities are shown patrolling the town streets to protect trick-or-treaters from getting a polar-bear surprise treat.
Since the National Geographic series moved from commercial network TV, underwritten by a forward-thinking Gulf Oil grant, National Geographic specials have become the top-rated programs on PBS. With their large audiences now a mainstay for PBS, one hopes that Gulf is not contemplating a move back to network TV where the show would probably flounder when matched against shows like ''Three's Company.''
One thing bothers this viewer: the indignity suffered by those glorious lumbering creatures as they are shot with tranquilizers, tagged for scientific reasons, and released into the wilderness, some with radio transmitters attached. Is treating polar bears as mere subjects of scientific research really preserving them in their natural habitat?