Dusk is the loveliest time in the bush of southern Africa. At Mgamo Camp, Zimbabew, a breeze is stirring. The sky is soft lace -- pinks, yellows, pale blues. Wildebeests, zebras and buffaloes graze in the distance. Indifferent lions lie among the rocks in an acacia grove. Before dawn, they will dine on wildebeest.

It is one of those evenings you know will stay with you as long as memory lasts. We sit around a little campfire -- my son; Alan Elliott and Dick Pitman, our guides; and a businessman out of Salisbury. The tents are raised, the African cooks are busy, the drinks are good. We are alone, 45 miles from the main camp in Wankie.

Last light comes quickly and just as quickly large shapes are silhouetted dimly against a nearby tree line. Elephants. They move single file toward our camp. The pace is slow and strangely majestic. Cows, calves, bulls.

The first cow looms up by the cooking tent, glances about, picks her way between the two sleeping tents, then vanishes into the bush.Over the next half-hour the herd follows one by one. We count 48 in the file. The 49th is a straggler, a confused young bull who has lost his way and is coming on toward the Land Rover where we are standing. Alan flashes a light. The bull rears back, bellows and trots off into the night.

Sleep comes early. Our snoring is an alien sound, a dissonace to the lion and jackal songs.

There is a tranqulity, a sense of purity here that gives a superficial insight into the minds of the eco-freaks and the true believers of the Sierra Club. To sit in the sun and watch lions, full bellies sagging, stroll back from a fresh kill is marvelous stuff. But there is an artificiality to it. This vast game reserve -- 5,600 square miles -- is not primordial. It is an immense farm, managed and harvested by man.

One afternoom we come upon a foot patrol of three game scouts, a European and two Africans. They are carrying semiautomatic rifles and have just shot an injured wildebeest. We provide a knife to cut off the animals tail, which is prized as a fly brush. There is a lot of laughing and joking about it. One of the Africans was a Selous Scout in the old Rhodesian army. His exploits in tracking guerrillas during the war are local legends. Like most of the game scouts, he's a tough nut.

The real job of these men is to protect the game from African poachers, to preserve the species and herds for posterity -- which means, in the short term, to perserve them for the enjoyment of white tourists like me. These perservationist policies create political, psychological and economic problems that Dick Pitman describes in an accompayning article. To oversimplify, they are polices that allow a white American to shoot an animal as a trophy and prevent a black African from shooting an animal for food. That is an intellectually troubling proposition. But a few days after leaving Ngamo, I got another side of the story.

Norman Carr is a sturdy, sunbaked middleweight who had been leading game safaris in Zambia for several decades. He's written books and is regarded as an authority on African wildlife. I found him in a small office on a side street in Lusaka where he has established the Save the Rhino Trust.

His obsession is the Luangwa River valley in western Zambia, an area of 56,000 square miles that has supported an enormous elephant population for centuries and contains what Carr describes as "the last surviving, viable population of black rhino in the world." The valley is sparsely populated. The land is unsuitable for farming because of of tsetse fly infestation. It is inaccessible for lack of a network of roads. Its wildlife, theoretically, should be secure from human predators. But since the early 1970s, by offical estimate, the elephant population has been reduced from 100,000 to 50,000. The black rhino population has been reduced from 8,000 to 1,500.

The problem is not the poor peasant who kills an animal to feed his family. It is rather caused by commercial poaching gangs armed with automatic weapons. They slaughter animals by the thousands, rip the ivory tusks from the elephant, cut the rhino horn and leave the carcasses to the vultures.

It is a profitable business. Ivory brings up to $50 a pound. Rhino horn has the market value of gold. It's in great demand in the Far East as an aphrodisiac and for medicinal purposes. In Yemen, it's prized for dagger handles.

The slaughter is not confined to the Lauyangwa Valley. Herds are being decimated in Zaire, Uganda, Chad and Angola. The killing is not on the scale we experienced in the United States in the last half of the 19th Century when out buffalo population was reduced from 60 million to less than 1,00 by 1900. But it is serious enough and the proximate causes are the same -- financial greed and weaponry. The long-range Sharps rifle did in the buffalo. Automatic weapons, abundant all over Africa, are doing in the elephant and rhino. Government indifference or inattention is another factor as it was in the United States a century ago. Game preservation is not a high priority budget consideration in most African nations. Finally, land hunger by growing populations in need of food is reducing wildlife grazing lands, as also happened in our own country. Iain Douglas Hamilton, the distinguished Kenyan wildlife scholar, believes land hungar is an even greater threat to the elephant of Africa than the automatic weapons of th poaching gangs.

Norman Carr responds to all this with his personal crusade to save the rhino. He has the full moral and partial material support of the Zambian government. The World Wildlife Fund has sent money. Prince Philip of Great Britain has given him an endorsement. He has put his own resources into the effort.

What is involved, basically, is the creation and assignment of properly equipped units to patrol the game area of the Luangwa Valley. The two units now in action arrested more than 300 poachers last year but the killing goes on. "Only the most urgent and drastic measures," Carr has written, "can save one of the last viable populations of black rhino on this earth."

Neither Carr or his Rhino Trust nor the essentially all-white conservation groups in Africa and elsewhere will save the unique wildlife species of this continent. Africans must do that out of a sense of self-interest that transcends the interests of pleasure-seeking tourists in funny hats. It is an uncertain proposition that they will do so.