A LOT OF people talk about overpopulation; a comparative handful does anything about it. And that handful has not as yet accomplished much. Despite the best efforts of numerous international organizations and various government initiatives, world population still continues to surge at the rate of about two million a week.

How do you slow down, let alone stop, the relentless increase of humanity? The best idea I've heard in a long time is to do it with money. To be precise, bank accounts. One for every woman in the world.

In America, the plan would work like this: When a girl reached puberty, she could -- if she freely chose to do so -- notify a local public-health office. At that point, a financial clock would start ticking. If she went a year without getting pregnant, the government would put a check for $500 in her account. No strings: She could take it out the next day and spend the whole thing, start a personal scholarship fund for college, or whatever she liked.

If she then went a second year without getting pregnant, the government would increase her annual payment to $600. The third year would be $700, and so on, reaching around $1,200 at age 20. Participation would be totally voluntary, and the payment non-discriminatory. A millionaire's daughter and a welfare kid would be treated exactly alike.

Suppose a young woman who has joined the plan decides that she wants a baby? There is nothing to stop her. Of course, she wouldn't get a check in the year she becomes pregnant. But payment would resume the year after, starting back at $500 and again slowly building.

What would this all cost? Less than you might think. Suppose that the plan went into operation next year and that 90 percent of American girls who reached puberty in 1991 chose to join. Suppose further that not one of those two million 12- and 13-year-olds got pregnant. In that case, the total cost in payments would be approximately $1 billion, plus another $2 billion or $3 billion to set up and staff the public-health centers.

Assume that in 1992 we again enrolled 90 percent, and so forth for five years; and that in all that time, not one of those participating had a baby. That would mean a maximum possible payment in the fifth year of about $10 billion. That may seem like an enormous sum. But it's less than the state of California alone will spend on Aid to Families with Dependent Children in one year.

In the District of Columbia, it costs $30,000 to $40,000 per year to raise one disturbed child in a group home. Most of such children now in care were born to teenage girls who should never have had the burden of motherhood thrust on them so soon. By contrast, $900 (the amount that the plan would pay a D.C. 17-year-old who had never gotten pregnant) seems pretty small.

In my own small state of Vermont, a 19-year-old mother with two children will get about $10,800 in cash and food stamps from the state this year. The $1,100 she would have received under the plan if she had never been pregnant begins to look like a real bargain.

A few months ago I published an outline of this plan in a national magazine. I received hundreds of letters in response. Some agreed. Some hated the idea -- chiefly, it seemed, those who don't yet believe that overpopulation is threatening the health of the planet. A few called it a proposal for "genocide." Their argument: Since the black and Hispanic birth rates in the United States are much higher than the white birth rate, the plan might produce a disproportionate reduction of minority population. But even if each ethnic group's birth rate wound up the same, this completely voluntary program would hardly be genocide. It would be gen-equality.

But could such a project ever get started -- here or anywhere else? Or is it just one of those ivory-tower ideas that looks good on paper but would never happen in the real world? An Investment in the Future As it turns out, the plan is already working in at least one American city. It costs even less than the ivory-tower version. And it provides additional benefits.

In 1986, Planned Parenthood of the Rocky Mountains began a pilot program of paying young women not to get pregnant. It has since become known as the Dollar-a-Day Teenage Pregnancy Prevention Program. Twelve young women in Denver formed the original group. Their average age was 15. Four were already mothers; four others had had abortions.

These young womenwere invited to come to a weekly meeting. Each got $7 if she came and was not pregnant. (The group uses the honor system. There are no pregnancy tests.) They also got soft drinks and cookies. Some of the young women came from homes so poor that they said they would have attended just for the food.

But a third motive soon developed: The young women rapidly formed a support group. The doctor who ran the program never lectured; she listened. In the end, the group had 18 members, of whom 15 finished the two-year program without getting pregnant. And without having any more abortions, which some might well have had.

In January 1988, Rocky Mountain Planned Parenthood started a second group in the same neighborhood. Ten young women joined and so far none has become pregnant. Meanwhile, two more groups have been organized. Some of the young women in these programs have clearly had their expectations of life raised. "I wasn't expecting to have a baby so early," said Anna, a 16-year-old with a 9-month-old son. "I want to have more children, but not right now. Maybe when I'm 30." Anna used her $7 a week to buy diapers. Another girl in the group, asked about her plans, said simply: "Graduate from high school. Go to college."

The total cost of the program is $365 per year per young woman, and another $250 apiece for administration. By comparison, the average early-teen pregnancy costs Colorado taxpayers around $13,000.

Already there is a similar group in Rocky Ford, Colo., and one in San Mateo, Calif. Plans are afoot for several in Florida and one on the Eastern Shore of Maryland.

This plan decreases abortion, saves taxpayers money and plainly benefits the young women it serves -- while at the same time making a start toward keeping the planet habitable. Is that ivory-tower stuff? Or plain common sense?

Noel Perrin teaches environmental studies at Dartmouth College.