The Food and Drug Administration is planning a new policy under which it would approve additives deemed safe for human use, even though they contain trace amounts of known carcinogens.

The agency already has applied the proposed policy to one additive, the food coloring Green-6, which contains a tiny amount of a chemical that is known to cause cancer.

Under the so-called Delaney Clause the FDA is required to ban additives that may cause cancer in humans or animals, no matter how slight the risk.

FDA spokesman Bill Grigg explained that as testing procedures have become more sophisticated scientists have been able to discover trace amounts of carcinogens in substances that are considered safe.

"The thinking is," Grigg said, that unless a new policy is applied, "the science of detection will force us to ignore what we say we're doing or blithely eliminate scores of products every time someone tests them with new techniques."

In the case of Green-6, explained Robert Lake, regulations coordinator for the agency's Bureau of Foods, the additive was tested and "came out clean."

"However, we know there is a chemical that crops up in the manufacturing process and is present in low levels," he said. "The Delaney Clause was satisfied when we tested Green-6. Nevertheless, we have to concern ourselves with the carcinogen in there. Under our previous way of regulating, it would not have been approved."

The Delaney Clause has been under attack for some time, particularly since 1978, when the FDA tried to ban saccharin after tests showed that it could cause cancer in mice. Several bills are pending in Congress to modify the food safety laws to give the FDA more flexibility.