A rare look at the horror that is Cambodia today will be offered this evening at 10 on WETA-TV.

On the whole it is a disappointment. The cinematography is mundane and the narration is low-keyed and eminently forgettable.

For a documentary that claims to be the obituary of a people, "Cambodia: A Nation is Dying" has about as much dramatic tension as a tale about the village pump breaking down.

An exception is provided by pictures of undernourished children: One boy, apparently a teen-ager, whose biceps are not bigger than a man's thumb. A younger boy too apathetic to brush the flies away from his face.

Their eyes wander vacantly, silently speaking volumes of pain and tragedy. Their images sear the brain.

The physical and political restrictions on Swiss journalist Hans-Peter Stadler and his camera team must have been enormous. Nevertheless, the piece cries out for greater spontaneity on the part of the photographer. The scenes are simply those that day's shooting schedule called for.The narration drones on, reciting the litany of disasters as if it were the specifications for the Phnom Penh sewage treatment plant.

There are some moments that come across with special force despite the blandness of the overall production. One in particular shows what apparently is a group of Cambodian civil servants dutifully taking notes as their Vietnamese adviser gives them a short course in administration.

The script places the chief responsiblity for Cambodia's plight on the Khmer Rouge government of Pol Pot. Occasionally it does take a shot at the new government of Heng Samrin and his Vietnamese patrons for their concentration on ensuring the peasant's political loyalty rather than on his need for food.

In one brief but telling sequence the narrator mentions that one small village has five Vietnamese advisers, or one for every member of the village council.

Following the sequence from Cambodia, a needed look at some of the international issues involved is provided by Stanley Karnow and Elizabeth Becker. Lest you think you can turn off your set shaking your head at the incomprehensible perfidy of the Chinese, the Soviets, the Vietnamese and the Cambodians, Becker will remind you that the United States, too, has had a role in bringing Cambodia to its present tragedy.