Thanks to a heedles decision by the Reagan administration, millions of needy people in the developing world will be denied family planning aid. This will occur because the Agency for International Development, under strong White House pressure, has cut off funds to the International Planned Parenthood Federation, the largest voluntary family-planning organization in the world.

The administration's decision to deny the IPPF the $17 million earmarked for it in this year's budget has no basis in any change in the law governing foreign population aid. For 11 years, that law has forbidden the use of U.S. aid for abortions. The IPPF insists it has scrupulously adhered to that law. It performs no abortions, does not advocate abortion as a method of birth control and, in distributing aid to independent national family-planning associations throughout the world, it is careful to warn that the U.S. allocation must not be used for abortions.

Less than 1 percent of all the money flowing through the IPPF is used for abortion-related services, and it is used by only 10 of the 119 participating nations. Moreover, the administration, which has administered the population program for the past four years, does not claim that the IPPF has violated the anti-abortion strictures. The administration simply decided last summer to reinterpret the law to please a group of extremists that wanted to change the pattern of family planning aid to developing countries. The new interpretation was specifically rejected by the House in language incorporated into the appropriation bill passed by both houses this fall. It holds that no money can be given to the IPPF if any of that money flows to foreign family-planning agencies that, using other sources of money, provide abortion-related services.

Essentially this means that the United States, which is only one of 27 donor nations, is trying to dictate family-planning policies for all 119 member nations. Like the United States, many donor and recipient countries have legalized abortion. Adhering to a policy that would effectively prevent these sovereign countries from establishing rules for their own national organizations puts the IPPF -- and the United States -- in an untenable position.

Losing the American quarter-plus of its financing will mean that the IPPF -- the single or major source of family planning aid to many Third World countries -- will have to cancel or sharply cut back family planning and other public health programs in some of the poorest countries of Africa, Asia, Central America and South America. As a result, many desperately poor women will resort to self-inflicted or illegal abortions, which are still major birth-control methods in the less-developed world. This avoidable suffering will be in large part attributable to this decision, which contravenes congressional intent.