BEHIND the stark reality that the world's population surges by 11,000 every hour of every day, there are hopeful new developments.
Across most of the developing world, a quiet revolution is taking place that marks the beginning of the end of an era of unprecedented population growth. Using new technology and innovative advertising campaigns, governments and private groups have begun tapping into a huge latent desire for smaller families.
The result, a sharp increase in the use of contraceptives and a corresponding decrease in the size of the average family, has far surpassed the expectations of population experts. A dramatic success story, it is one of the singular developments of the postwar era.
"Once the world got serious about offering quality family-planning services, fertility declined rapidly," says Joseph Speidel, president of the Population Crisis Committee in Washington. "The trend belies the notion that population growth is an intractable problem or that fertility declines depend on major economic and social changes."
Among the large global community of population experts, satisfaction is tempered by the recognition that, for now, lower fertility translates only into slower growth rates, not an actual decline in world population, which is not expected for a century or more. Indeed, says a United Nations report, "four decades of the fastest growth in human numbers in all history" lie ahead.
"Things aren't as bad as they would have been, but they're still getting worse," says Philip Claxton, a former State Department adviser, who was the first special assistant on population issues.
An era of declining birth rates began during the 1960s and '70s when national leaders first grasped the implications of overpopulation on economic development and living standards.
Armed with two revolutionary new contraceptives, the birth-control pill and the intrauterine device (IUD), dozens of fledgling public and private family-planning agencies launched forth with an equally revolutionary message: Family size is a matter of choice, not fate.
The results have been dramatic. Worldwide, contraceptive use has jumped from 8 to 50 percent since the 1960s.
In turn, fertility rates - that is, the average number of children per family - have dropped from 6.1 to 3.9 in the developing world, halfway to a "replacement" level of 2.1 per couple, which is approximated in many industrialized nations, according to the World Health Organization.
Achieving the other half will be more difficult: The rate of decline has slowed since the 1980s.
Abetted by strong economic growth, fertility declines have been sharpest in East Asia. Largely excluded from the trend has been sub-Saharan Africa, where women still bear an average of six children and less than 5 percent of whom, in many countries, use modern contraceptives, according to estimates by Macro International in Silver Spring, Md., an organization that does fertility and family-planning surveys.
With 25 years of experience in hand, family-planning experts say the keys to success are easy to identify and frequently transferable.
The most critical variable is consistent, visible support for family planning by political leaders.
"The main element of success is commitment from the top," says John Bongaarts, research director of the Population Council in New York. "Leaders have to be on TV repeatedly saying, `Overpopulation is bad for us.' "
The other precondition is innovative ways to serve people who, in developing countries at least, are likely to be uneducated, immobile, and fearful or suspicious of birth-control methods.
Meeting the need usually requires social-marketing, such as popular TV soap operas that now air in many countries with educational messages on the virtues of small families. It also means having accessible hours for clients, repeated counseling, and delivery services, like the team of 700 paid community-based distributors who deliver birth-control pills and condoms to villages by bicycle in Zimbabwe.
Like dozens of other nations, Zimbabwe has also sought to provide a mix of birth-control technologies ranging from condoms to sterilization to long-term injections and implants.
"We want to do what we call the cafeteria approach to family planning, giving people the whole range of contraceptives," says Yoshiko Zenda, director of the United Nations Population Fund in Zimbabwe, which is one of Africa's few family-planning success stories.
In a few countries, governments have used legal measures or coercion to put backbone into population programs.
For example, China has used peer pressure and heavy fines to enforce its controversial one-child policy. Tunisia has outlawed marriage for men under 20 and women under 18, a step that has proved effective in lowering the number of children per woman.
According to Population Council estimates, the world has nearly half a billion fewer people today thanks to the family-planning efforts launched a quarter-century ago.
In future terms, the implications are more dramatic, says Mr. Bongaarts. Without the reduction in fertility rates produced by family-planning programs since the 1960s, the world a century from now would contain 4.6 billion more people, an additional number roughly equal to the current world population.
Today the demand for family-planning services still outpaces the supply because of funding shortages, religious opposition, civil conflict, or - in the case of some Gulf and East Asian nations - outright government support for larger families.
Only half of all women in the developing world have access to family planning. Worldwide, excluding China, 100 million couples who want to delay or stop having children have no means of doing so, the Population Council says. The result will eventually be tens of millions of unwanted births.
If the unmet need for family-planning services were addressed, experts predict, the result would be a worldwide contraception-prevalence rate of 65 percent. That would lower fertility to just under three children per family - a significant step closer to the replacement-level fertility that would stabilize world population at a tolerable plateau.
Lower birth rates aren't the only benefit. Family planning can significantly reduce the number of deaths caused by complications from pregnancy and childbirth that, according to the World Health Organization, now total 500,000 annually.
Increasing birth intervals to more than two years, another goal of family planners, can sharply reduce infant mortality, doctors, say.
"Family planning could bring more benefits to more people at less cost than any other single `technology' now available to the human race," says a recent UNICEF report.