NGOZI, BURUNDI -- Jim and Anita Pauwels of Weatherford, Tex., came to the mountains of central Africa to teach Hutu people how to farm fish. They figured it made more sense than watching videos and saving for ski trips.

They sold their house, four cars and six acres of land, and gave away the cats and dogs. They went to Norman, Okla., for 10 weeks of fisheries training. They went to eastern Zaire for three months of French lessons. Then they came up here to the rain-drenched forests, cold nights and bad roads of the Burundi highlands. They soon discovered that if you want to talk fish with the locals, you must ride a motorcycle in mud.

"We were like the Marx brothers. Every day we would get up, take our bikes out and fall over in the muck," said Anita Pauwels. "I had been here six months, when I had my worst fall. I hit my head on a tree, and the farmers laughed at me. I said to myself, 'That's it. I am going home.' "

Instead of going back to Texas, the 35-year-old artist and her husband, a 45-year-old mechanical engineer, got better on the bikes. In the past 15 months, they have helped 1,000 Burundian farmers build 190 fish ponds. About 15 tons of mountain-grown tilapia fish will be harvested next month.

When president John F. Kennedy launched the Peace Corps 26 years ago, it caught the fancy of tens of thousands of young Americans who had more idealism than skill, more energy than experience. Since then, as the idealism of young Americans has waxed and waned, the Peace Corps has moved into middle age with more and more volunteers, like Jim and Anita Pauwels, who are not so young.

The average age of a volunteer in the 1960s was 24; now it is 30. Eleven percent of volunteers are more than 50 years old, compared to less than 1 percent in 1964.

In the 60s, a volunteer was usually a liberal arts graduate who was sent into the field to teach English and an ill-defined type of work called community development. Now he or she -- the ratio of men to women is 1-to-1 -- is more likely to be an experienced welder or math teacher or crop pathologist.

Many early volunteers were sent abroad, armed with vague notions of doing good and little else. Host countries often complained about energetic, but unskilled young Americans who did not speak the local language. Most volunteers now arrive with working language skills and nuts-and-bolts techniques for teaching poor people how to make stoves, set up small businesses, grow rice, farm fish.

As it has evolved, the Peace Corps has developed an international reputation as one of the world's most effective grass-roots development organizations.

In "Reversing Africa's Decline," an influential paper by the Washington-based Worldwatch Institute, the Peace Corps is held up as a model for other developed countries attempting to alleviate Africa's acute shortage of skilled people. That model confines itself to projects -- fish farming is a favorite example -- that can be sustained and replicated after the volunteers go home.

Worldwatch proposes blatant imitation of the Peace Corps on a worldwide scale, with a multinational assistance corps funded by the World Bank.

Despite a steadily improving reputation abroad, the Peace Corps has weathered bad years at home. After the Vietnam war and Watergate, voluntary service to the U.S. government fell out of fashion. Peace Corps applications tailed off, the agency's budget was reduced and the number of volunteers in the field fell by two-thirds.

For a decade the Peace Corps was absorbed, and seemed to disappear, into Action, an agency that coordinated all federal volunteer programs. It was reborn as an independent agency in 1981 by order of President Reagan.

In good and lean years the Peace Corps has remained an organization for Americans who are willing to live as poor people live. Sub-Saharan Africa is the poorest region in the world; in the past seven years more than half of all volunteers have gone there.

One-quarter of those sent abroad do not stick out their two-year assignments. They go home early for a variety of reasons -- medical, emotional, linguistic. Those who stay can look forward to diarrhea, to cultural isolation and loneliness, to making very little money. If they farm fish on a motorbike in the mountains, they can look forward to falling in the mud.

"I think older people make better volunteers. They know more. They accept small failures. They are more flexible," said Jim Pauwels, who served in the Peace Corps in India when he was in his early 20s.

Pauwels, who is on leave from his job at General Dynamics in Fort Worth, where he builds radar systems, said: "I think I did a much better job this time."

That assessment is shared by many Peace Corps administrators, by foreign governments who host the volunteers and by specialists in development. The consensus among development professionals is that the current generation of Peace Corps volunteers is of a much higher caliber than their predecessors.

"The volunteers I see today are much older and much more culturally sensitive than in the 60s. They are committed to development and more serious about accomplishing things. You see fewer people who come to float around," said Godfrey Cherono, a Kenyan who has worked with volunteers in that country since 1969 and is now associate director of the Peace Corps program there.

A longstanding virtue of the Peace Corps is that, compared to other agencies that send Americans or Europeans abroad for development work, it is a bargain. It costs the U.S government about $20,000 a year to keep a Peace Corps volunteer in the field. An employe of the U.S. Agency for International Development costs about $100,000 a year.

"For the dollar, the Peace Corps is by far the most cost-effective program I know from the U.S. government," said Amare Getahun, an Ethiopian development specialist who for the past six years has supervised volunteers in an agroforestry project in Kenya. Getahun's assessment echoes that of many senior U.S. diplomats who have served in Africa.

Amare said the willingness of American volunteers to go into the field and demonstrate agroforestry techniques, which mix trees with food crops for high sustainable yields, has motivated scores of Kenyan government extension agents to do likewise.

"When these Kenyans graduated from the university with a degree in agriculture they wanted titles and desks to sit behind," said Getahun. "Seeing the Americans go out every day into the field changed their attitudes. The Peace Corps is the reason this agroforestry project has translated itself into a successful government program that Kenya is committed to keeping."

This record of solid work at a bargain price has impressed Congress in recent years. Despite Gramm-Rudman budget restrictions, Congress has mandated the expansion of the agency from its present 5,300 volunteers to 10,000 by 1992. The agency's $130 million annual budget is expected to be increased by about $10 million a year for the next six years, according to Alixe Glen, a Peace Corps spokeswoman in Washington.

Country directors in Africa, where much of the expansion will be focused, recently have received word from Washington that they should expand their training capacity.

Back in the United States, the agency has recaptured some of its 60s glamor. In 1985, in response to Africa's worst-of-the-century famine, Peace Corps Director Loret Miller Ruppe appealed for 10,000 volunteers with farming skills. About 20,000 people responded, although only 5 percent had the needed skills.

According to the agency's office in Washington, there were five qualified applicants last year for every volunteer position.

The immediate financial rewards of Peace Corps work remain low. Volunteers are paid a living allowance that varies by country. In Africa it ranges from about $175 to $280 a month. When they return home, volunteers receive a lump-sum readjustment allowance of $175 for each month served.

Money, volunteers say, is beside the point.

"I was at the top of the wage scale, but it just wasn't fulfilling," said Greg Moser, 26, a diesel mechanic from Greensboro, N.C., who is assigned here in Burundi.

The first time he ever saw the word Burundi was when he read it in a letter from the Peace Corps. He rushed to the Greensboro public library and found the Maryland-size country on a map.

"I wanted do something to help people. I don't have a girlfriend back home. A lot of my friends said they wish they had the nerve to do this," said Moser, a graduate of Nashville Auto-Diesel College. "I got to the point back in Greensboro where I didn't care if I worked or not. I was just bored."

Dan Griffith, 37, leaves Burundi next month after two years. An experienced fisheries technician who had managed fish farms in several southern states, Griffith set up a fingerling operation here that supplied starter fish for new ponds. Griffith said he survived twoyears in Africa because he was not a do-gooder.

"If you come here with completely altruistic motivations, you won't last," said Griffith. "I leave Burundi knowing how to speak French well. That makes me more marketable.

"I have learned a lot about patience. I never read books much before I came. I never wrote letters. I learned how to enjoy my own company," said Griffith.

While Peace Corps pay is not worth much, the two years of experience is a valuable commodity on a resume, especially for former volunteers who want to work abroad, in international business or in Washington.

Former volunteers now make up 10 percent of every new Foreign Service class. Nearly 90 percent of new recruits for U.S. AID are former Peace Corps volunteers. There are 100 former volunteers working at the World Bank, 200 in staff jobs on Capitol Hill, 14 are vice presidents at Chase Manhattan Bank.

Jim and Anita Pauwels, one of 300 married couples serving as Peace Corps volunteers worldwide, are going back to Texas in September. He will go back to General Dynamics in Fort Worth and she probably will return to the art studio where she had worked making reproductions of western art.

They said they leave with a demystified and strongly positive impression of Africans.

"When we were planning to come here, we heard about 'African time' -- that nobody cares about doing things when they supposed to," said Jim Pauwels. "I soon learned that there is no such thing as African time. If I make an appointment to look at a farmer's fish pond and I am not there, plus or minus 15 minutes, he will go somewhere else. These people are busy trying to feed their families."

In an area where protein deficiency is a major dietary problem, where fish ponds had never been attempted, the Pauwels were extraordinarily successful.

"It took us nine months to get a few people interested and to build the first three ponds," said Anita Pauwels. "But after we brought in the first fingerlings, and people saw that we could do more than just talk about fish, they went crazy. One of Jim's farmers is working on his sixth pond."

Anita Pauwels was quick to learn French and Kirundi, the local language. When she wasn't on a motorbike in the mountains, she wrote and illustrated a pamphlet on fish farming. She also started a rabbit breeding project. She was named this year's outstanding Peace Corps volunteer in Africa.

Despite the success of the fish ponds, the government of Burundi this summer decided to halt Peace Corps involvement in the project. It gave no reasons, but diplomats speculated the government was nervous about unsupervised westerners freely moving around in rural areas. It is Peace Corps policy to accept such decisions without argument.

Normally, fish ponds are supervised by volunteers for six years before they are turned over to locals. Without that long period of training, Peace Corps' experience in other African countries indicates that fish farming does not become self-sustaining.

The Burundi government's decision means that, in the long run, the Pauwels' two years of work may well come to nothing. It is a chance every volunteer takes.

"We are quite upset. I know the program is going to fall a lot more than it should," said Jim Pauwels. "It is their country."