Africa has the world's highest birth rate, and one of the reasons is that many African governments view family planning as a western plot to sap their sole potential asset that is increasing -- their populations. Fear and suspicion are the rule.

Then there is Zimbabwe.

While other African leaders pay lip service, at most, to the idea, Prime Minister Robert Mugabe and his wife Sally have heartily endorsed birth control for this country. The result has been a family planning program that most experts contend is the largest and most effective in Africa.

It is operated by the National Family Planning Council, an autonomous, politically high powered group whose program director is Sally Mugabe's sister, Dr. Esther Boohene.

Despite the fact that Harare and Washington are at odds diplomatically these days, the United States has provided $8.5 million, a third of the program's cost.

The results have been impressive, statistically. Family planning officials recently produced a survey contending that 27 percent of Zimbabwe's married women are using modern contraceptives -- by far the highest percentage in sub-Saharan Africa. Nearly 3,000 women are being added to this roll each week.

Family planning programs are as delicate as rare wildlife in Africa. The subcontinent's first major program, launched in Kenya with World Bank financing in 1967, failed in part because it was tied to a companion project to increase the health of mothers and children. For various political reasons, most of the money went to the health component. The net result was that the program actually helped increase Kenya's population growth rate to its present record level of 4 percent.

Zimbabwe has learned from that error by keeping family planning separate from other health projects. But the program's very success has raised doubts among some medical experts. They contend that Zimbabwe, encouraged by western aid donors, has gone too heavily into birth control while neglecting other factors that affect the lives and health of its mothers and children.

The centerpiece of the program is a network of more than 600 community workers, who distribute pills and advice to thousands of women in hard-to-reach rural areas where many seldom see a doctor or hospital.

Each worker is trained for six weeks in Harare, then supplied uniforms, notebooks, pills, a bicycle, and a salary of $90 per month, a substantial income by rural standards and four times as much as the Ministry of Health pays its village health workers.

The council theoretically answers to the Health Ministry but in practice maintains its own management and institutional structures. It has its own Land Rovers, medications and other supplies, all provided by aid donors.

That separation from the large and unwieldy government health bureaucracy is both the program's strength and the source of many of its problems.

"There was much grass-roots resentment that family planning gets all the vehicles and the money," said a doctor who worked for the program for two years. "There was the sense that the family planning worker's job is to get as many people using contraceptives as she can. They're so concerned with giving it away that they don't always bother to explain what it's about or worry very much about side effects."

Encia Kachomba is a family planning worker whose clients are the wives of laborers on the big commercial farms just north of Harare. Most of the housing compounds she visits each month have no ventilated toilets or clean water supplies. Younger children in the area often display early signs of malnutrition.

But Kachomba said while she sympathizes with their plight, she is not trained to do more than recommend that an obviously sick child be taken to the nearest clinic. Her main task is to make sure that her clients get their pills on time each month, and understand how to use them.

She also is not trained to note possible side effects or to monitor the health of her "accepters." She advises all new clients to take a trip to the local clinic for a blood pressure test and examination that doctors say all women beginning to use contraceptives should have. But she concedes that many never go.

"If they don't feel sick, they don't go," she said. "They say they can't afford to lose a day from the work."

Boohene, a Ghanaian physician who moved here after independence, said the council is well aware of the problems. Its workers are gradually being retrained in child nutrition, oral rehydration therapy and other areas. But she resists calls from some quarters for the family planning to be integrated into the Ministry of Health.

"This has been a successful program, and breaking it up and integrating it will not allow it to remain," said Boohene. "On paper, it can be done. But I can tell you from experience that in real life, it just doesn't work."

But despite her political clout, even Boohene does not always get what she wants. For two years, family planning clinics dispensed depo provera, an injectable contraceptive that has been banned in the United States and much of Europe because of controversy over possible side effects.

Depo was the drug of choice for many Zimbabwean women, who feared that their husbands disapproved of contraception or did not like the daily regimen of taking pills. But there was no organized system for monitoring women for side effects. Last year, health officials banned it.

"It was an emotional thing," said Boohene, looking back with regret over the banning. "The women of Zimbabwe wanted it."