Ping a wine glass at your next dinner party and invite the company's attention to soil erosion in Africa. Very briefly, perhaps, you may be able to quiet the table. But your spouse is not going to let you do it again soon.

Actually, a part of the U.S. government did ping a glass, so to speak, and invite the company's attention to soil erosion in Africa back in 1978. Lester Brown relates in a new Worldwatch Institute study, "State of the World 1985," that the Agency for International Development reported Ethiopia was losing a billion tons of topsoil a year. It foresaw "an environmen- tal nightmare unfolding before our eyes . . . a result of the acts of millions of Ethiopians struggling for survival . . . ."

In due time the nightmare arrived, in Ethiopia and elsewhere in Africa. Television injected it into the mainstream of American consciousness. Lester Brown suggests that what Americans reacted to so instinctively and generously was not simply the spectacle of suffering and poverty but the spectacle of a systemic breakdown, a continent-wide overload of historic dimensions: too many people, too little food, and now the additional possibility that population growth is driving climactic change -- the number of people seeking to survive on marginal land is drying out Africa.

Is he right? A premonition is in the air that the deterioration is beyond the reach of relief (though relief is essential) and beyond the reach of development (ditto), that the laws of progress have been suspended across broad swaths of Africa and an indescribable long-term tragedy is in train. It is a tragedy that African leaders and publics themselves may be too distracted to do anything effective about.

We well-intentioned foreigners, meanwhile, will put in some conscience money and will continue to address the South Africa question, politically more urgent and potentially rewarding. Otherwise, we may quietly remove Africa from the list of places of full American engagement and slip into an undeclared policy akin to battlefield triage: That's when the medics, realizing they can't save all the wounded, tend first to those with the best chance to survive.

These are, as I say, vibrations in the air, not live options in any official policy papers I am aware of. Perhaps they represent an overreading of the current African scene. Certainly they represent a fundamental revision of an American outlook on the Third World that was blooming as few as 10 or 15 years ago.

I return to Lester Brown, whose book of 1972, "World Without Borders," caught many of us in a mood of readiness to move beyond the flawed political syndromes that had drawn us into Vietnam and to explore new and ansing modes of cooperation for peace and development in the international "community." The emerging resource squeezes of the period -- first of all the oil shock -- fitted in nicely. The environmental movement made its contribution of sensitivity. This was the wave that helped produce Jimmy Carter's victory over Gerald Ford in 1976. An Africa policy emphasizing a strong and positive American role in a continent on the upswing followed.

In public opinion as well as policy, the pendulum has since swung back toward a focus on a great-power political framework. This has happened for reasons largely unrelated to Africa. Few foresaw, for instance, that the "flickerings of universal consciousness" spotted, approvingly, in the 1970s by Harvard scholar Stanley Hoffman would come to settle not so much on economic development as on nuclear survival. But the effect on attitudes toward Africa has been substantial, and events in Africa -- the East- West proxy contests, the famine, the sense of headlong deterioration -- have reinforced the trend.

In the 1970s the idea came that Africa would profit greatly from a grand North-South "dialogue" to oversee a redistribution of international income and economic opportunity, but the idea went nowhere. It was replaced in the 1980s, at least in official American eyes, by the idea that the marketplace should be allowed to do its magic. But in Africa the promised fruits are not yet in view. Nor was there established in the more upbeat years a broad-based American political coalition able to see adequately to the continent's need for aid, credit and trade in the bleak years.

The coalition that has been assembled, however, is something. Assorted soft-hearted and hard-headed groups, in as well as out of the Reagan administration, have an interest in the continent's welfare. There may be no great ideas going but there is no fence around Africa, either. It is part of the world, part of us. Ping that glass.