Two members of an endangered species of mountain gorilla were shot and killed in a private preserve in the African nation of Rwanda, raising the possibility that poachers might be killing the animals for their heads.

At least one of the gorillas was decapitated and the other may have suffered the same fate, according to information received yesterday by the World Wildlife Fund. A cable received by a board member was unclear as to whether the second gorilla had been killed for its head, which poachers sell as trophies.

The cable came to Jeffrey Short in Chicago from Dine Fossey, a naturalist who has been living among the mountain gorillas in Rwanda for six years. Fossey's cable said the two gorillas had been shot along Rwanda's border with Zaire, a mountainous region Rwanda set up as a park for the animals.

Naturalists say there are as few as 200 mountain gorillas in the world, most of them in Rwanda. The mountain gorilla (called Gorilla gorilla) is the largest of the world's two species of gorilla (the other is the lowland gorilla) but is declining in numbers at an alarming rate.

The mountain gorilla grows to six feet and can weigh as much as 400 pounds. The male has a pronounced crest on top of its head that sets it apart from male lowland gorillas.

Its numbers have decreased because the mountain gorilla's habitat has been encroached by natives seeking new farm land and grassland and by plantation owners growing bananas.

Fossey said in her cable that she had no evidence that poachers had killed the gorillas, though the decapitation suggested they committed the crime. Plantation owners could have done it, since they have complained on occasion that the gorillas raid their banana trees.

Only 12 mountain gorillas reside in zoos. Five are in Antwerp, two in Chester, England, two in Cologne and three in Oklahoma City.

"I have no idea whey anybody would kill one of these creatures," said Theodore Reed, director of the National Zoo. S. Dillion Ripley, secretary of the Smithsonian Institution and chairman of the World Wildlife Fund, said, "I deplore the senseless destruction of one of the world's gentlest relatives of man."