The birth last week of the 5 billionth human to share our planet brings attention to the rapid increase of global population. Moreover, it raises serious questions regarding the durability of the earth's natural systems and resources.

The world is growing by an unprecedented 1 million people every four to five days, 85 million a year. Population has doubled in the last 35 years and it is projected to double again in the next 40.

Dr. Norman Borlaug, Nobel laureate and father of the green revolution, doubts the world's ability to feed an additional 5 billion people within the next four decades. Lester Brown, president of the Worldwatch Institute, offers overwhelming evidence that our planet's carrying capacity is already bursting at the seams.

But even if it could be proved that there is no correlation whatsoever between rapid population growth and the earth's eco-systems and resources, there still would be compelling reasons for encouraging lower birth rates: the health and very lives of millions of women and children in the Third World where 90 percent of the world population growth occurs.

Ten million infants die each year in the developing world. A major expansion of family planning services could reduce those deaths by half or more, according to findings of the World Fertility Survey.

An estimated 500,000 women in the developing world die each year as the result of pregnancy and childbirth complications. About one quarter of these women could be saved if unwanted pregnancies could be avoided, according to a Columbia University report.

The World Fertility Survey concluded that children born less than two years apart are much more likely to die in infancy or in early childhood than those whose births are spaced at intervals of two or more years. The pattern was present in all 41 developing countries included in the survey.

In Tunisia, Syria, Jordan, Yemen and Portugal, infants born less than two years apart are about 2 1/2 times more likely to die in their first year than children born 24 to 47 months apart. In these same countries, infants born less than two years apart are up to five times more likely to die in their first year than those spaced at intervals of four or more years.

Children born less than two years apart are twice as likely to die before reaching their first birthday in Bangladesh, Morocco and Turkey than those spaced 24 to 47 months apart.

Meanwhile, a substantial portion of developing world women already have all the children they want, according to the World Fertility Survey. The range varies from 12 percent in Ghana to 61 percent in Colombia and Sri Lanka. The average is about 50 percent. But a great majority of these women do not have access to family planning information or services.

A Columbia University report claims that avoiding unwanted pregnancies would have a considerable impact on reducing maternal mortality, especially since the proportion of women who want no more children rises sharply with age and with the number of living children.

This is most significant because older women and those who already have many children stand a higher risk of dying as a result of childbirth than do women in their twenties and those with only two to four children.

Data on maternal and child mortality in the developing world should be an essential factor in the current political dialogue on U.S. funding for international population programs. If existing family planning services are cut back or withdrawn, there is every reason to believe that deaths among women during pregnancy and childbirth as well as among infants and children born at less than two-year intervals will escalate considerably.

The U.S. Agency for International Development has withdrawn its funding of the International Planned Parenthood Federation, the largest nongovernment provider of family planning services for Third World women. And the future of U.S. funding for the United Nations Fund for Population Activities, the largest multilateral organization providing such services, is in doubt.

The blue-ribbon Committee on African Development Strategies has urgently recommended resumption of U.S. contributions to both IPPF and UNFPA as a key to slowing down population growth and preventing future famines in Africa, the region of the world with the highest fertility rates and the highest susceptibility to malnutrition, hunger and starvation.

Today's unprecedented world population growth is due primarily to a combination of declining death rates and the young age structure of the developing world, where more than half of the population is either in or entering its childbearing years.

Lower mortality rates have resulted in large measure from improvements in nutrition and public hygiene and advances in medical technology -- notably smallpox vaccinations, widespread use of antibiotics and malaria control programs.

While the full consequences of continued rapid population growth may be unknown, the choice the United States and the industrialized world must make is clear. By drastically cutting back or withdrawing international population assistance, we risk proliferating human suffering and chaos on a global scale and we would be signing the death warrants of countless women and children in the Third World.

Or we can substantially accelerate our long-standing commitment to the most effective and humane solution for reducing rapid population growth -- voluntary family planning assistance -- and reduce infant mortality by one half and maternal motality by one quarter. If we are ready and willing to meet this monumental challenge, our legacy to future generations will be an opportunity for a better quality of life and the achievement of greater human dignity.Werner Fornos is president of the Population Institute, a nonprofit public education organization.