In the central marketplace of this capital city, a bag of charcoal that 10 years ago sold for about $2 now costs more than $10, because the supply of wood used to make it has grown scarce.

To the north and west of the city, vast stretches of once thick forest "are now in danger of becoming deserts," according to Tanzanian President Julius K. Nyerere.

While the industrial world has been adjusting to the new, post-OPEC economics of oil, coal and nuclear power, Africa and the rest of the Third World have been experiencing a different kind of energy crisis: lack of firewood.

On a continent where most homes lack electricity and most people seldom see a car, wood is the poor man's main power supply. It cooks his food and heats his home, and it accounts for three-quarters of Africa's energy usage.

But a generation of bad forestry management, poor agricultural practices and the relentless pressure of rapid population growth is threatening to turn much of the continent into a deforested wasteland.

In Tanzania, where experts say as much as 94 percent of total energy consumption is from wood, the United Nations Food and Agriculture Organization warns that 1 million acres of woodlands are being lost every year, a trend that could strip the entire country of trees in 20 years. "The magnitude of the fuel wood scarcity is to us no longer a crisis but a catastrophe," said Tanzania's minister of natural resources, C.G. Kahama, in a recent speech.

The FAO says that more than 100 million people in 26 countries -- 18 of them in Africa -- already face acute shortages of fuel wood, and it classifies 1.2 billion others as living in "deficit" conditions.

The growing scarcity of fuel wood is the energy problem in much of Africa," said a 1980 World Bank report that predicted "potential fuel wood crises" in all but a few African countries during the next generation.

The meaning of those grim statistics can be seen throughout the subcontinent.

Around the northern Nigerian city of Kano lies a 25-mile radius of barren land where trees and shrubs once flourished. Similar expanding rings of wasteland surround other West African cities, including the Senegalese capital Dakar, Ouagadougou in Burkina Faso and Niamey in Niger.

In Kenya, a recent study indicates that women, traditionally the main gatherers of fuel wood, are spending between 20 and 24 hours each week searching for wood. In Botswana, women are trekking as far as eight miles each day, while in northern Ghana, it takes a full day to gather enough wood for nine fires.

Another Kenyan study says that Nairobi's urban poor spend as much as 30 percent of their incomes on cooking fuel. In many cases, they pay more for the fuel than for the food they cook. One reason is that truckers are hauling charcoal from as far away as Sudan because of shortages inside Kenya.

Even in Zimbabwe, where use of fuel wood is far below the African average, a consultant's report released this week warned that three of the country's eight provinces are being stripped of trees to the point where in another generation, they may have no wood at all.

Deforestation is just one of the ways the wood shortage is damaging Africa. Lack of fuel also affects public health.

Drinking water does not get boiled, and huts are kept cold at night. In the Sahel region of West Africa, according to Earthscan, a London-based, U.N.-supported development institute, families have cut back from two hot meals a day to one, and in some cases to one every other day. In Burkina Faso, soybeans introduced for nutritional purposes have been rejected because they require too much cooking.

Food production also has been hurt. Earthscan estimates that families across Asia, the Middle East and Africa are burning 400 million tons of animal and agricultural waste each year that could serve as fertilizer to grow more food. One study estimates that Africa loses 20 million tons of grain annually for lack of fertilizer that is burned for fuel.

Equally important, the growing loss of trees and vegetation has helped speed the process of desertification, which is eating up 24,000 square miles of fertile African land each year, according to the United Nations, and claiming vast tracts of land in several countries, includingSudan and Tanzania as well as the Sahel region.

Western experts and aid donors were slow to grasp the nature and dimensions of the fuel wood crisis.

John Spears, senior forestry adviser at the World Bank, was quoted recently as conceding, "In the late 1970s, after 25 years of almost exclusive focus on the industrial value of forests and extensive programs for pulp mills, sawmills and industrial plantation forestry, it was belatedly realized that such programs were doing little for the vast majority of the rural and urban poor of the developing world."

The World Bank and other donors have since jumped headlong into the problem, pouring more than $500 million into community forestry and related efforts during the past seven years.

But, as in many aid programs, analysts are now stepping back and questioning many of the assumptions they made when first attempting to cope with the problem.

One of those assumptions was that a crash program of distributing energy-efficient cooking stoves could help head off the crisis. But few African peasants have showed interest in purchasing or using anything but the cheapest and most basic stoves made from readily available local materials.

At the same time, analysts have begun to reexamine their earlier belief that domestic cooking and heating was a major cause of deforestation. They have now concluded that other factors -- especially the indiscriminate clearing of woodlands to create new farm land and grazing areas and, in some places, use of wood for commercial or industrial purposes -- are far more important. It is generally agreed that while more efficient stoves can save money for their owners and provide a cleaner living environment, they have little impact on forestation.

Even tree planting, a seemingly unchallengeable activity, has come under criticism in some countries. The most popular planting variety has been the eucalyptus, a fast-growing and hardy species that provides good timber and pulp for paper. But critics say that the trees deplete soil nutrients, use too much water and fail to provide the products most needed by poor peasants -- food and fodder.

The debate is a complex one, and often there are hidden factors. A U.S. forestry program in Senegal found villagers were not interested in growing trees for fuel wood but were eager for trees that would provide shade and fruit -- varieties that the program had not made available. Earthscan reports that a World Bank forestry project in Niger failed when villagers destroyed seedlings because they had been planted on traditional grazing grounds.

Above all, like so many other African problems, the fuel wood crisis is a function of poverty. Those with money can afford higher prices for wood or can switch to other fuel sources such as kerosene or coal. But the poor have no such alternatives. For them, writes U.S. environmentalist Erik Eckholm, "the real energy crisis is a daily scramble to find the fuel they need to cook dinner."