It now appears that the cheetahs are very poorly equipped for such challenges. As it is, the cheetah, with worldwide population estimates ranging from 1,500 to 25,000, has been classed an endangered species. Its ability to reproduce, at least in captivity, is seriously limited.

Fifty of those whose blood was tested were at the De Wildt Cheetah Breeding and Research Center in Pretoria, but they or their parents had been captured in the northern Transvaal and Southwest Africa, now known as Namibia. The five others were from zoos.

In one of the tests, conducted at the National Cancer Institute's Laboratory of Viral Carcinogenesis in Frederick, Md., red blood cells from all 55 cheetahs were subjected to a gel electrophoresis technique that sorts out enzymes in terms of their response to an electric field. As a rule, no two people or animals carry enzymes that are almost all identical genetically.

Of 47 indicators of enzyme composition widely used in assessing the genetic diversity of cats, mice and human beings, all were identical in all the animals tested. In these and additional tests more than 200 enzymes and other proteins were assessed and almost all proved identical. Problems With Reproduction

The study was financed by Friends of the National Zoo in Washington, D.C., in hope that it could be learned why cheetahs in captivity have such a low rate of reproductive success. It was found that even in wild cheetahs sperm counts were only 10 percent of those in domestic cats. Furthermore 70 percent of the sperm were abnormal. Both traits typify extensive inbreeding.