MANY RECENT VISITORS to rural areas in the Third World have encountered small biogas plants - locally constructed tanks that convert animal dung into methane gas and fertilizer. The methane produced in these plants is a clean efficient fuel for cooking and heating, and the high-quality fertilizer is free of the pathogens originally in its ingredients. Some 4,300,000 biogas plants have reportedly been built in China in the last four years, many of them large, communal affairs. In Korea, Pakistan, Kenya, and Costa Rica, the devices blend so well into the local surrounding that few visitors are aware of the shadow of a white-haired Englishman by the name of E.F. Schumacher looming behind them.

Biogas plants are examples of what development specialists call "appropriate technologies." The meaning of this term can be illuminated by contrasting an appropriate technology with an "inappropriate" one - inappropriate, at least, for certain conditions.

In India today there is a crying need for nitrogen fertilizer. A large coal-fueled fertilizer factory will produce 230,000 tons per year; 26,000 biogas plants are needed to produce the same amount. But the biogas plants would cost $15 million less to build, and all this money would be spent inside India, saving $70 million in foreign exchange. The biogas plants would provide 130 times as many jobs, and these jobs would be located in rural villages, where most people live and where employment is most desperately needed. Biogas plants would also produce the fertilizer where it is needed, eliminating the transportation requirements form the centralized coal plant. Finally, the biogas plants would produce enough fuel each year to meet most of the energy needs of 26,000 Indian Villages, while the coal-fired plant would consume enough fuel every year to meet the energy needs of 550 villages.

Biogas plants, in short, meet the criteria set forth in the bible of appropriate technology, Small is Beautiful: "Technology of production by the masses, making use of the best of modern knowledge and experience, conducive to decentralization, compatible with laws of ecology, gentle in its use of scarce resources, and designed to serve the human person instead of making him the servant of machines."

The name of E.F. Schumacher has become synonymous with appropriate technologies. And as his ideas gained currency and influence, he became something of an international celebrity. Before his death last September. Schumacher had seen appropriate technologies programs established by the United Nations Environment Programs, the World Health Organization, the U.N. Development Program, the U.S. Agency for International Development, the State of California, a dozen Third World countries, and a score of research institutes around the world.

Ernest Friedrich Schumacher was already in his sixties when his best seller, Small is Beautiful , was published in 1973. He was one of that rare handul of economists who, in fellow economist Herman Daly's phrase, "care about what counts, not about what is merely countable," Deeply disturbed by many of the underlying values and assumptions that both undergird and shackle his own professional discipline, he subtitled his book: "Economics As If People Mattered."

E.F. Schumacher was one of the earliest Western critics Of the "trickle down" approach to economic development - the belief that if rapid economic growth could be achieved the problem of poverty will take care of itself. On the contrary he argued, rapid increases in GNP can often leave the majority of the population worse off in absolute terms. What is needed is not mindless growth, but programs that are tailored to the culture, resources, and aspirations of each particular region.

When, in the summer of 1965, Schumacher began hosting small London gatherings to explore the concept that eventually became known as appropriate technology, he appeared a most improbable candidate to become an underground cult hero. A former Rhodes Scholar and chief economic editorial writer for The Times of London, he had spent most of his adult career as the economic advisor of the National Coal Board in England - the bureaucracy that manages the nationalized coal mines.

But perhaps the connection of his origins to his destiny had a certain logic after all. England, as George Orwell wrote, was "founded on coal, more completely than one realizes until one stops to think about it . . . Practically everything we do, from eating ice to crossing the Atlantic, and from baking a loaf of writing a novel, involves the use of coal." In 1950, the United Kingdom obtained 90 per cent of its energy from coal. This might be contrasted with the 44 per cent for all energy that the United States now gets from oil, our principal fuel. The Coal Board' economist necessarily had to develope a wide range of interests.

Small is Beautiful attests to the breadth of Schumacher's interests. Essentially a collection of essays, the book details the author's thoughts on such desparate subjects as "Peace and Permanence," "The Proper Use of Land," "Nuclear Energy," "The Problem of Unemployment in India," and "buddhist Economics." The underlying theme that binds all these topics into a cohesive whole is a relentless concern for the social values that underpin technological choices. He emphatically rejects the proposition that technology is, or ever could be, value-free. "No matter what tune you play on a piano," he once remarked, "it will still be paino music. His gospel is "technology with a human face."

During the last two years of his life, Fritz Schumacher devoted much of his energy to a book that, he felt, would be much more important than Small is Beautiful . Published posthumously, A Guide for the Perplexed is Schumacher's final word. He uses the volume to set forth his views on the "big" issues: the existence of God and the meaning of life.

As with his earlier work on technology run amok, Schumacher is exploring a theme of great current interest to persons 40 years his junior. His purpose in writing this book is to sketch an intellectual "map" of the terrain he has travelled so that others may follow the path to his conclusions without first spending a lifetime exploring deadend streets. Schumacher believes in a higher order of being. As a consequence, he believes that the Good Life is not the one extolled in Pepsi ads but rather a life of spiritual elevation guided by experience and faith.

In essence, Guide is one man's statement of belief. It draws eclectically from many religious and mystics and imposes a loose structure on the resulting array of quotatings. The result is a sometimes odd blend of Thomas Aquinas and Nyanaponika Thera, of Dante and Edgar Cayce.

Many who enjoyed the crisp logic of Schumacher's earlier work will be disappointed, and even embarrassed, by elements in the new book, which appears unlikely to become the sort of bible for the newly religious that Small is Beautiful has become for appropriate technologists. But as the summation of an unusual man with a vast range of interests, it could be a useful touchstone for some who are perplexed by the inability of western materialism to satisfy a nagging void m the soul. The "map" will be interest even to those who don't find the treasure where Schumacher says it is buried. The book is an appropriate final note for a man who always wore a human face behind his economist's mask.