Development in the Third World is never an easy task and is usually fraught with perils.

Debt-ridden Zaire is often regarded as a case study in Western-assisted development gone wrong, but it actually provides examples of both successful projects and failures.

In one project, Peace Corps volunteers are helping to add protein-rich fish to the diet of thousands of people in the central African nation's vast inland where malnutrition is common. In another, the U.S. government and American banks have helped finance a billion-dollar power line to carry electricity to an area that does not need it.

The stories of these projects illustrate the promises and pitfalls of Third World efforts to modernize poverty-stricken societies. Their problems almost serve as a definition of backwardness: lack of roads and fertilizer, inefficiency and corruption, and economic dependence on a single mineral or agricultural product whose price may fall and disrupt years of planning.

The happier story is centered on telapia, a tropical fish that sells for as much as $6 to owners of home aquariums in the United States. The fish can reproduce 60-fold in a year and grow to eating size of about six ounces within six months.

Telapia supplements the staple of the Zairean diet, a root called cassava or manioc, which is poor in protein. Meat is almost unknown in the diet, because cattle are scarce, and one egg can cost 50 cents. As a result, most Zaireans average only 80 to 85 percent of the recommended daily minimum of 1.5 ounces of protein.

The Belgians began fish farming during the colonial days but used only natural methods, which will produce about six to seven pounds per 100 square yards of pond.

More than 40 Peace Corps volunteers have taught hundreds of farmers to more than triple production by feeding manioc leaves and cornmeal to the fish, and by using manure and wastes from their truck farms as compost for the ponds.

The Peace Corps started with seven fish farming volunteers in 1974. By 1980, production from fish culture had increased by almost 300 percent, according to country director Bill Pruitt. Farmers trained by the volunteers have sharply raised their income, and children eating the fish grow faster than those who do not.

Production could be increased another four or five times, according to Peace Corps fish experts, if phosphate fertilizer and rice bran could be used. Transportation is a constant problem, however, and Zaire must use valuable foreign exchange to import all its fertilizer.

In the second development story, Zaire has spent $1 billion to construct the 1,100-mile Inga-Shaba power line, which is scheduled to start operation later this year.

It is the longest direct current line in the world, and a Western diplomat described the technology as "22nd century." Electricity is to be carried from generators at Inga near Kinshasa to the southern Shaba province in the heart of Zaire's copper belt, where the power will be converted to alternating current.

The problem is that Shaba has no use for the electricity, while power-starved communities along the line are unable to tap the direct current without building expensive converter stations.

When the project was designed, copper prices were at a record high and Zaire was seen as having great growth potential because of its mineral wealth. President Mobutu Sese Seko apparently also saw the project as a way to keep control of Shaba.

Today, the bottom has fallen out of the copper market, and investment has virtually dried up after two civil wars in Shaba in 1977 and 1978. Because electricity is of no use to people living near the line, they tend to find their own uses for it -- removing parts of the metal towers to make beds, shovels and other equipment, according to one diplomat.

The cost overrun on the project is overwhelming, about $500 million in a country that is already strapped with $4.5 billion of debt. Some of the extra expense is most likely due to the incompetence and graft that trouble the entire country, according to foreign analysts here. Many Western diplomats are convinced that Mobutu makes certain that nothing works very well to make it more difficult for any group below him to challenge his rule. By cutting in the elite on the spoils of a thriving black market, the theory goes, he also coopts potential rivals.

The funding for the project has been supplied by the U.S. Export-Import Bank and private American and European financial sources headed by Citibank and Manufacturers Hanover Trust. The West has poured money into Zaire to keep the copper and cobalt mines running in Shaba, and to support Mobutu as a bulwark against communism in black Africa. Much of the planning went awry because of the 1974 collapse of prices for copper, Zaire's main foreign exchange earner. The price per pound tumbled from $1.40 to 60 cents and is currently about 75 cents. Growth was also stymied by the invasions of the Shaba by secessionist Katangan forces who crossed the border from refuges in Angola.

So the grandiose project has so far turned out to be a white elephant, while the low-key fish-farming endeavor has already made visible improvements in the lives of several thousand people in a similar period of time.

To start a pond from scratch, a farmer simply buys 100 or more 3-inch fingerlings for about 4 cents each. In six months, when he drains the pond, he should have about 4,000 fish, including fingerlings to restock, if he has followed the Peace Corps formula.

For their output, the ponds require very little area and far less labor than a seasonal crop. Weather is normally not a problem.

The 40-acre farm of Kashiama Kitenu Ya Nkalu, 300 miles west of the capital of Kinshasa, demonstrates how much fish farming can alter a family's lifestyle. Kashiama, who "has seen 50 rains," is the Rockefeller of peasant farmers in the Kikwit area, with 12 ponds that produce $75 dollars or more in profit a month.

His mud brick house, freshly whitewashed for a visit by a foreign journalist and Peace Corps volunteers, has a rare cement floor. The walls are adorned with animal skins and pictures of Mobutu, of Kashiama's family and of four Peace Corps workers. Pride of place is given to a chiming pendulum clock and a transistor radio with tape deck, which was blaring out the Marlboro cigarette commercial tune during the visit.

He has two wives but only three living children. Nine others have died, one at 18, the rest all "little folks."

The youngest child, 5 years old, was named Pasi, meaning "hard" in the local Kikongo language because he was Kashiama's first child in 11 years to survive infancy. Half a head taller and much healthier-looking than his 7-year-old playmate Ntaba, Pasi is living evidence that his family's diet is better than most. Ntaba, the son of a farm worker, has three of the telltale signs of malnutrition: distended stomach, an orangish tinge to his hair and a dull, glassy-eyed look.

Without fish culture, Kashiama says, he would barely make a profit, although there is obviously some exaggeration for the benefit of his Peace Corps guests. He also grows bananas, pineapples, coffee, sugar cane, corn, manioc and palm nuts.

Still, a Sunday harvest of his smallest pond demonstrates what a difference fish farming can make for a peasant.

When drained, the 120-square-yard pond netted 33 pounds of fish. Women came from miles around and jostled to buy 1.5-pound packets for about $1.50 -- far less than the price of meat even when it's available.

Peace Corps volunteer David Reside, an aquatic biology graduate of the University of Illinois, advises Kashiama on construction and maintenance of the ponds. Most of the volunteers use motorcycles to make the rounds of their 30 farmers, but there is a shortage, so Reside walks throughout an area with a radius of about 20 miles to see his in"clients."

Kashiama's harvest from one pond is worth the equivalent of a 175-pound sack of coffee. He gets only about eight sacks of coffee a year, however, compared to 24 fish harvests.

The Peace Corps volunteers work directly with about 1,200 farmers in the country. Because of a "spread effect," the corps estimates that an additional 4,000 farmers have indirectly learned about the method.

Director Pruitt has requested another 45 fish culture specialists, which would double the size of the program, but he is concerned that the farmers will become too dependent on the volunteers.

The volunteers are supposed to train Zairean counterparts to take over their jobs eventually. But the farmers fear that their countrymen would extort fish or money from the people they are supposed to be helping, abuse the motorcycles and generally cause the program to deteriorate, volunteers said.

Although the investment is small, the stake for Zaireans is large.

"If every village had four or five farmers with ponds, it would make a huge difference in the diet," said volunteer Fred Marton, who has spent four years fish farming in Zaire. "People who now don't eat any animal protein would be able to have it a couple times a week."

Such an achievement, he added, could take 20 years.