COROICO, BOLIVIA -- On the humid mountainsides north of La Paz, the United Nations is using doctors and road-builders instead of bullets and jails to curtail the cultivation of coca, the base for the cocaine that is flooding into the United States.

This approach contrasts with the U.S.-assisted efforts of the Bolivian government to disrupt trade by driving out the coca traffickers through helicopter sweeps of the areas where coca paste is converted chemically into the narcotic. The United States is financing such anti-drug police units in Bolivia and Peru, which together produce 90 percent of the world's coca.

The United Nations Fund for Drug-Abuse Control is to spend $22 million over the next five years persuading 10,000 peasants in the Yungas region that the benefits of development assistance -- aimed at converting their land to production of coffee or oranges -- outweigh the profits from cultivating coca. So far, it has had mixed results.

But U.N. officials hold that the police-sweep approach only sows anger and violence. They note that many peasants and soldiers have been killed in the Chapare, Bolivia's biggest coca-growing zone, where the anti-drug police are based.

The U.N. approach is to persuade entire communities, with the inducement of several forms of aid, to agree not to grow more coca. As coca plants die after their 20 years of productivity, an area would thus become coca-free.

In the meantime, doctors are to treat the tuberculosis and parasites found in the peasantry and to teach mothers about prenatal care to reduce the 25 percent infant mortality rate. U.N.-financed teams also are to repair schools, link isolated communities to the region's unpaved trunk road and provide low-interest loans to grow the coffee and oranges instead of coca.

Coca-growing in the Yungas dates to colonial times. Indians in Bolivia's tin and silver mines and wind-swept plateau of the Andes have chewed the green leaves for centuries to ward off cold and hunger.

The bigger obstacle to the U.N. effort is coca's profitability, up to five times more than any other crop. Farmers have rushed to meet the rising U.S. demand, with coca production in the Yungas increasing from 25,000 acres in 1970 to about 83,000 today, according to a program official.

Further hampering the U.N. effort have been rumors spread by drug traffickers that the aid workers will require coca growers to burn their crops without compensation. At one point, peasants occupied the U.N. office here to demand that the organization pull its 100 aid workers out of the Yungas.

After meeting with communities and patiently explaining the project's purpose, the U.N. team has succeeded in persuading growers in 53 of them, covering nearly 10 percent of the Yungas' population, to join in.

According to Fernando Miranda, the team's leader, 200 additional communities have asked to participate in the project only to be turned down for lack of funds.

U.N. officials said that in the past year they have improved 15 miles of dirt roads, provided potable water to 20 communities and vaccinated 2,500 children. Miranda said that farmers will plant 1,500 acres of coffee this year and forgo planting 3,000 acres of coca.

"We have shown that you can halt the spread of coca-growing through persuasion rather than force," Miranda said. But the great expectations created to persuade communities to participate appear to have left many peasants disappointed with the results.

For the community of San Pedro, the United Nations has built a safe water system and improved the road. But the 200 residents are getting restless because the organization still has not repaired the school, built a soccer field or constructed a promised clinic.

"We're still willing to abide by the agreement we signed, but some people are beginning to raise questions," said resident Julio Mamani.

The community of Mumaypata has no electricity, potable water or schoolhouse. But residents Martin Irillondo and Eusebio Poma are not about to sign the agreement to participate in the U.N. program.

"Other communities have told us that they don't come through with what they promise," said Irillondo.

U.S. Embassy officials say most of the communities working with the United Nations are in the part of the Yungas where not much coca is grown.

"We've met a lot of resistance in the big coca-growing zones," acknowledged Mario Cuellar, a U.N. official in Coroico.

Despite the problems, U.N. officials and many independent observers call the program a success.

"Just getting coca farmers to stop expanding their production, as the U.N. program has done, is no small feat," said a western diplomat.