To the Editor:

Re "Mother Nature's Pesticide Factory" by Michael Fumento (Op-Ed, June 9): Environmentalists are correct in wanting to ban potentially toxic chemicals, and Carol Browner, Environmental Protection Administrator, is equally justified in seeking a revision of the Delaney Clause, though not for the right reasons.

Since 1958 the Delaney Clause has allowed innacurate and misleading data to steer regulation. Until the flawed methodology behind its guidelines is replaced, humans will continue to be industry's real guinea pigs, irrespective of the chemicals tested.

There are some 70,000 chemicals on the market, almost half in common use. Of these, only 800 have undergone standard rodent tests used to try to predict human cancer risks.

The cost of running a typical pre-chronic and long-term rodent carcinogenicity bioassay is $1.6 million to $2.5 million per chemical in 1986 dollars. With more than 25,000 commonly used chemicals awaiting evaluation, to test them all would cost $50 billion to $75 billion, not counting inflation and administrative costs.

As we have seen in the case of such pharmaceuticals as thalidomide and Bendectin, and chemicals that commonly find their way into our food chain like Alar, Captan and Lindane, animal tests do not prevent these chemicals from being marketed.

The diverging opinions of scientists, regulators and private research organizations about rodent bioassay results have too often led to repeated testing of the same chemicals at various doses in different species. Each new generation of testing further delays regulation and allows the proliferation of potentially dangerous chemicals in our environment.

While many toxicologists believe that completely replacing animal tests remains in the future, many are merely reluctant to abandon familiar methods to explore new ground. Countless nonanimal technologies around the world are awaiting validation, while others have been validated and used. X-ray technology has been used, with human cells and subjects, to measure the mutagenic effects of chemical agents accurately.

These modern and often technically superior methods are not only cost-effective, but also allow the dangers of individual chemicals to be observed in a few hours or days, as opposed to the 8 to 10 years needed for rodent bioassays.

Ultimately, if our aim is to protect human health, we need fewer pesticides, fewer food additives and fewer toxic ingredients in household products and cosmetics. These are not the myopic desires of "environmental extremists," as Mr. Fumento suggests. They are universally embraced by concerned individuals everywhere who want to protect their health and the environment. ALIX E. FANO Washington, June 11, 1993 The writer is a researcher for the Physicians Committee for Responsible Medicine.