AN investment that offers one of the highest social and economic returns to developing nations is money spent on encouraging family planning. A few economists believe the world population explosion will take care of itself. For example, Friedrich A. Hayek contends that as people in the developing countries become more affluent and sophisticated, they eventually decide to have fewer children. He notes that the annual rate of population growth in these nations peaked at about 2.4 percent in the mid-1960s. It's about 2.1 percent today.
But that drop is less than some demographers predicted. Most population experts hold that more active family planning measures are needed.
The World Bank expects the world's present population of 5 billion to double before it levels off early in the next century. Ten billion is a lot of people. The world's poor are already pushing on the doors of some industrial nations, seeking entry as refugees or immigrants (legal and illegal). The pressures will get far worse in coming decades, especially if hunger spreads.
``It is imperative that developing countries renew and expand efforts to limit population growth,'' says Barber Conable, World Bank president. His institution is examining what more it can do.
``The most you can do is provide options, encourage governments to give their people a choice in limiting their fertility,'' says Susan Cochrane, a senior population economist at the World Bank.
Many developing countries are reluctant to borrow World Bank money for birth-control programs. Though loans are available through a sister organization, the International Development Agency, at very favorable terms, they must be repaid. Nations would rather get grants for population programs from the United States, the United Nations Fund for Population Activities, the Scandinavian countries, and some of the rich countries.
Considering the economic, social, and political threats from too rapid population growth, these funds are not adequate. A study for the US Agency for International Development figures that population programs need an extra $300 million a year for the next 20 years to tackle the problem properly.
Otherwise many developing countries will be overwhelmed. For example, Africa's most populous nation, Nigeria, will see its citizens multiply from about 100 million today to more than 600 million.
Anecdotal evidence multiplies of problems related at least partly to excessive population growth.
Algeria, with half its population under age 20, has violent riots. Many rioters are frustrated, unemployed youths. Their nation's economy can't create jobs fast enough. Brazil's burgeoning populace chops down the Amazon jungle for farmland, threatening the world environment. The Nepalese bare their hills of rain-retaining forests, prompting disastrous floods downriver in Bangladesh. Overpopulation and poverty in El Salvador lead to civil war. The list goes on.
Mr. Conable notes that population policy touches upon ``sensitive cultural and religious values.'' Ms. Cochrane says government leaders must be ``more courageous'' in tackling the problem. They can talk about health concerns (dangerous illegal abortions, higher child mortality when births are spaced too close, etc.), or the difficulties of educating huge numbers of young people and finding them jobs.
Her positive message: ``There are cost-effective and humane ways of bringing down fertility.''