Each year, American firms export from 100 million to 150 million pounds of pesticides that cannot legally be sold or used inside the United States.

This situation understandably bothers Sen. Patrick V. Leahy of Vermont, who has introduced a bill that would mandate an end to the export of banned and unregistered pesticides.Up to a point, it can be argued that other countries are masters in their own houses, that Washington does not always know what's best and should not try to tell other governments how to protect their own citizens. For that matter, some of the unregistered pesticides being sold abroad were developed for pests, crops, and climates that don't even exist in the United States.

Even so, Congress should still pass the Leahy bill not as a favor to the citizens of other countries but to keep Americans from being poisoned by the banned pesticides. That's what can happen when the United States imports fruits and vegetables treated with exported U.S. chemicals that American farmers can't legally use on their own crops.

Ideally, international standards governing pesticides should be toughened. But that isn't likely as long as such standards are set by an obscure, Rome-based group called Codex Alimentarius. As Cox News Service reports, 42 per cent of Codex pesticide residue standards are weaker than their U.S. counterparts. The Codex limit on DDT residues, for example, is 50 times higher than the U.S. limit.

Tougher screening of foreign produce brought into the United States would obviously help, too. But that couldn't be accomplished without a massive and costly increase in the federal bureaucracy responsible for such screening.

As matters are now, the Food and Drug Administration is able to test only about one percent of the one-million shipments of produce imported each year. Admittedly, the FDA could make more efficient use of its limited import inspection program. For example, when it conducts inspections, the FDA looks for only about half of the pesticides known to be used in the exporting countries. When illegal pesticide residues are found, the FDA is reported in a 1986 congressional study to fail half the time to impound the tainted produce.

But even if such flaws were corrected, there still would be sharp limits to what stepped-up inspection could accomplish. So much foreign food is being imported that it would be impossible for the FDA to hire enough inspectors.

That leaves Sen. Leahy's bill as the only practical alternative if Americans are to be protected from foreign produce treated with chemicals banned in the United States. In the words of the Vermont lawmaker:

"If the Environmental Protection Agency says a chemical is too unsafe for use on U.S. farms, then it's too unsafe for use on foreign-grown foods that will be imported and end up on America's dinner tables."