Like the missionaries of an earlier era, they came to Africa bearing a new faith. But instead of the Bible, they preached the gospel of western technology in an often puzzling argot of industrialization schemes and integrated development plans.

There was one East African nation that attracted them more than any other.

Poverty-stricken Tanzania, once one of the most neglected ornaments in Britain's colonial crown, became the centerpiece of one of this century's great social experiments. The vision of a leader, President Julius Nyerere, joined with the funds and expertise of some of the western world's largest institutions in an attempt to remake a country and lift it out of poverty.

Western countries, led by the World Bank, have poured more than $2 billion into Tanzania since 1970, more than they have given to any other African nation. They hoped to create a model for the Third World to follow. Instead, Tanzania has become a symbol of technology and good intentions gone awry, of experts who lost their way, of poor people who became poorer.

A country that once had been able to feed itself and whose farmers had produced surpluses large enough to sell overseas collapsed into chronic dependency on western grain and emergency food shipments.

Tanzania joined the long list of African nations dependent on food handouts for survival in 1979. It has remained on it ever since.

Africa's food crisis long has been viewed as the result of drought, poverty, domestic politics and ill-advised government policy. Now, an increasing number of analysts, including international aid workers themselves, have come to the conclusion that western assistance has also inadvertently compounded the crisis.

In Tanzania, western donors first emphasized industrial development at the expense of the farming sector. Later, when they turned their attention to rural areas, donors often devised schemes that were too costly and too technologically sophisticated for what the World Bank lists as the 14th poorest nation in the world.

The schemes have littered Tanzania's rural landscape with the remains of factories, farm machinery, roadways and water pumping systems that the country lacks the money, spare parts and expertise to operate or maintain.

Food aid programs provided cheap western grain that depressed the prices that were paid to local farmers for their grain and allowed the government to postpone necessary agricultural reforms. Aid has had a corrosive effect on the Tanzanians themselves, instilling what Canadian analyst Roger Young of the North-South Institute in Ottawa described as "a deep-seated psychological dependence . . . . Local solutions and domestic resources are often seen as inferior."

There is, of course, a positive side to this aid. Donors helped provide the funds for the country's ambitious primary school program and for its successful effort to build health clinics within walking distance of every Tanzanian village. Recent grants and loans have helped keep the country from economic collapse.

But a decade of large doses of aid has done little to arrest Tanzania's agricultural decline. In some instances, combined with dubious government policies, the aid may have helped hasten it. Per capita food production during that decade has fallen 12 percent. Production of cash crops such as coffee, cotton, sisal and cashews has fallen at equal or greater rates. The value of these crops is also down, in part because of declines in world prices. The quality of these crops, too, has deteriorated due to poor storage, delays in planting and harvesting and breakdowns in the transportation system.

"Aid became the equivalent of what oil was for Nigeria," said Goran Hyden, a Ford Foundation analyst who spent a decade in Tanzania. "The urge to do good in Africa is now an albatross around the neck of Tanzania."

Ironically, Tanzania's agricultural decline may have begun in 1967, when Nyerere launched a campaign for national self-reliance and economic equity. While socialist-oriented, the campaign advocated a peaceful, voluntary transition to socialism. It was a marked contrast to the forced collectivization schemes of the communist world. Western donors found it very attractive, and they found Nyerere to be an eloquent and persuasive spokesman for the Third World.

Western money flowed. Tanzania received $51 million in aid in 1970. A decade later, the annual amount had risen to $625 million. By then, aid accounted for two-thirds of the country's development budget.

At first, the idea was to recreate the Marshall Plan in Africa. "They thought it was just a matter of pouring money into big projects and, presto, something would happen," said Stephen Gurman, director of the Canadian University Services Overseas office here.

Unlike postwar Europe, Tanzania is a land of peasant farmers who eked out a subsistence from traditional food crops such as corn, millet, cassava and sorghum, or from selling cash crops like coffee, cotton, sisal and cashews. Farmers are not only the country's backbone, but its arms and legs as well. They make up 90 percent of Tanzania's population and produce 85 percent of its exports.

By the early 1970s, it was clear that Marshall Plan-style development -- heavy industry programs, road building and large hydroelectric schemes -- was creating a fragile and superficial shell of progress while bypassing the peasants. The economy did not take off. It stagnated. Many of the new roads and factories quickly fell into disrepair. It was then that the World Bank, under the leadership of Robert McNamara, offered a change in direction. 'Basic Human Needs'

The new strategy became known as "basic human needs," and it was designed to offer peasants incentives and services that would improve the quality of their lives, draw them out of a subsistence mode of living and into the modern cash economy and help them produce more.

For the government, an important element in this new strategy was the process of "villagization." Peasants were relocated from scattered homesteads into consolidated self-help village communities. The government first attempted persuasion and later, when that failed, coercion to get peasants to resettle. By 1977, nearly 90 percent of the rural population had been relocated in 8,300 villages.

For social services -- schools, clean water facilities and health clinics -- villagization made good sense. But for farming, it was a disaster.

The new villages were often miles from traditional fields, and peasants were forced to abandon land they had worked for generations. Village sites were chosen more for their accessibility than their fertility. Many proved to have bad soil, which often was overplanted to a point where it became useless. The problem was exacerbated by the harsh drought that struck during the height of the villagization campaign in 1974, and later by massive floods.

While the government was resettling the peasantry, it also was consolidating its control over the farm economy. In 1976, Nyerere abolished the country's 2,500 local cooperative unions, arguing that many were corrupt, inefficient and politically uncontrollable. In their place, he established a series of state-controlled corporations, known as parastatals, that were given legal monopolies to supply peasants with credit, tools, fertilizer, seeds and other needs. Parastatals could buy crops, store them and sell them on the world market.

Parastatals, however, soon proved to be even more mismanaged than cooperatives. Unlike the cooperatives, they were answerable only to the central bureaucracy in Dar es Salaam, not to the farmers themselves.

The companies ran up big deficits and quickly soaked up most of the country's investment capital. According to the World Bank, 90 percent of capital expenditures in agriculture between 1975 and 1982 went to the parastatals. By 1982, 11 crop marketing boards had lost a total of more than $200 million.

In most businesses, falling behind schedule is unprofitable. In farming, it can be fatal. In Tanzania, the failure of the state boards to supply seeds, fertilizer and tools to the fields on time meant many crops went unplanted.

The fate of the once-thriving cashew crop illustrates the combination of forces that has crippled farming here. In 1975, Tanzania was the world's second-largest cashew producer, exporting 120,000 tons of raw nuts. But villagization moved many cashew farmers far from their groves, while low government prices for their crop and delayed payments from the state cashew authority gave them little incentive to trek back to the groves to harvest or to plant new trees.

Compounded by drought and plant disease, the result was that by 1983 Tanzania's cashew harvest had fallen to 32,000 tons, nearly one-quarter that of 1975.

Western aid donors were not the architects of either the villagization or parastatal policies, but many became their willing backers. Between 1974 and 1982, the World Bank provided $174 million in easy-credit loans to six crop and marketing boards. A confidential World Bank study two years ago concluded, "The lending experience shows that due to overwhelming problems both internal and external to the parastatals, this assistance has had little if any positive impact."

Donors made other mistakes as well. The World Bank lent Tanzania more than $10 million to help expand the country's cashew-processing capacity. As a result, Tanzania in 1982 had 11 factories capable of processing three times as many cashews each year as the country currently grows.

Six of these plants are now idle, in need of spare parts. Five others run at less than 20 percent capacity. Domestic processing costs are so high that the U.S. Department of Agriculture estimates that it is cheaper for Tanzania to send its raw nuts to India for processing. Overly Complicated Projects

There were many other aid projects too complicated to work in Tanzania. Canada, at Nyerere's behest, established a 70,000-acre wheat farm in northern Tanzania using ultramodern farming techniques and Canadian-built combine harvesters. Critics contend that the $35 million project is so complex that Tanzanians will never be able to operate it without Canadian aid.

Canada also built a modern, automated bakery in Dar es Salaam. It is designed to turn out 100,000 loaves of bread daily, but it needs new parts and usually operates at less than half capacity. A United Nations consultant has estimated that Tanzania could have built 10 smaller, less mechanized bakeries for the same price and that they would have produced the same amount of bread while creating four times as many jobs.

Rural aid projects were misconceived for a host of reasons. Many donors felt compelled to spend big money quickly to justify the size of their staffs. For some, including Canada and Denmark, funds lapsed at the end of each fiscal year, resulting in a last-minute rush of approvals. Donors often were required to stipulate use of equipment made by suppliers back home. That meant peasants, accustomed to cattle-drawn plows and hand hoes, received tractors and combine harvesters.

According to the World Bank, more than half the 2,663 tractors and combine harvesters belonging to farmers' groups in 1981 needed spare parts and did not work. As a result, a half million acres of land could not be cultivated. Peasants complained of a nationwide shortage of hand hoes.

Few donors were equipped to ascertain what peasants really might want or need. "It's not very pleasant to spend a month in a peasant village, so people tend to do a lot of their program development from offices in Dar," said Gurman of Canadian University Services Overseas. "They take a quick field trip and pass through villages in a cloud of dust. A lot of important little details can get ignored."

Few donors anticipated the precipitous economic decline that drained Tanzania of nearly all its foreign exchange. When westerners handed over the keys to their projects, there was often no money for parts or fuel to keep them operating.

The United States, which has provided $356 million in aid to Tanzania since 1953, has not been identified with the worst of the donors' white elephants. But critics say American food aid, totaling more than $150 million, has played a role in depressing prices paid to local farmers.

Most of the food has wound up in cities such as Dar es Salaam and has contributed to the growth of a dual food system. Rural areas generally feed themselves but provide little or nothing to the cities. The cities, in turn, have lived off cheap food supplied from overseas. Analysts in Dar es Salaam estimate that as much as 80 percent of the city's food comes from imports or aid programs.

Some experts believe Tanzania's peasants are growing enough food to feed the entire population of 20 million, but are withholding much of it from the legal market because official prices are too low. Accurate figures are hard to come by, but Tanzania's Ministry of Agriculture has estimated that 25 percent or less of the corn and rice harvested is sold to state marketing boards.

Much of the rest is said to go to the lucrative black market, which offers as much as three times the official price. The rest disappears over porous borders to countries like Zaire or Kenya, where prices for some crops are higher.

In the past, the government has tried to force peasants to sell the state more of their produce. Roadblocks were set up in the cashew-growing areas of the south. Peasants were allowed to pass only if they could prove they were on their way to their groves for harvesting. Officials in other areas set mandatory production quotas, and, in some cases, fined villagers who fell short. New Policies Announced

Coercion having achieved little, the government recently has moved to increase dramatically producer prices. Between 1980 and 1982, corn and rice prices rose 50 percent and wheat prices 75 percent. Although 30 percent annual inflation wiped out the real gains, new increases of as much as 40 percent were announced in June by Finance Minister Cleopas Msuya. He also announced an ambitious program to reduce the size and power of the parastatals and reinstitute the cooperative unions that were abolished eight years ago.

No one can say whether such policy changes will turn Tanzania around. Some donors are enthusiastic -- others have their doubts. "We're like educators," said a senior western aid official here. "We go from enthusiasm to enthusiasm, and we like to shout slogans as we run down the halls. There gets to be a bandwagon effect. This year, we're all on a private enterprise kick."

Having spent so much and bought so little, many donors now are cutting back. Countries such as Sweden -- Tanzania's single largest donor -- and Canada have not increased aid levels in three years despite the 90 percent jump in inflation here during that time. The World Bank, which at one time was pumping in more than $100 million a year, has cut back to less than half that figure. Bank officials privately have made clear there will be no increase until the government comes to terms with the International Monetary Fund over further economic reforms. The United States has suspended all future aid funding, except for emergency food relief, because the Tanzanians have failed to pay an $8 million debt.

Tanzania's government would like more aid. But even some officials admit now that aid was a mixed blessing that ended up increasing the country's dependency on the West.

"It's our fault at least as much as the donors because, after all, we agreed to their projects," said an aide to Nyerere. "We were nearly always talked into highly sophisticated, ultramodern machinery that we couldn't maintain. We ought to have been firm and said no."

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