The Food and Drug Administration said yesterday that it plans to ban the use in animal feeds of certain antibiotics used to treat infections in humans.

The FDA's reason is that routine, long-term use of germ-killing drugs in animals can lead to the development of bacteria that resist antibiotic treatment - first in the animals, then in the humans that handle meat, eggs and milk.

Commissioner Donald Kennedy has made his immediate target penicillin, to be followed by tetracycline and ultimately by other antibiotics whose routine use in feed can build resistance to therapy in humans.

Although thorough cooking can kill the bacteria, an agency spokesman said that people who handle antibiotic-treated products are put at risk.

"The goal of the proposed regulation is to preserve these antibiotics' effectiveness as medical treatments," the agency said.

The FDA began allowing the addition of antibiotics to feed, mainly to stimulate growth, in 1955. The practice long has been controversial. More than a decade ago, the New England Journal of Medicine warned that "unless drastic measures are taken very soon, physicians may find themselves back in the pre-antibiotic Middle Ages in the treatment of infectious diseases."

The proposed penicillin ban affects feed mainly for 35 per cent of the nation's swine and 10 per cent of its chickens and turkeys. The drug will remain available to treat disease in the animals.

Antibiotics less likely than penicillin to produce bacterial resistance may be substituted, the FDA spokesman said. If these prove less effective than penicillin, which he hold Associated Press is unlikely, the ban could raise prices to consumers - an estimated five cents per person per year.

The reason is that producers would need more time and more feed to bring animals up to market weights and might also lose some to disease that would have survived on antibiotic-treated feed.

Possibly reflecting a stricter regulatory stance brought to the FDA by Commissioner Kennedy when he joined the agency a few months ago, Dr. C. D. Van Houweling, director of the Bureau of Veterinary Medicine, said the use of penicillin in feed confers benefits on the livestock industry and the public that do not outweigh the long-term hazards to human health from proliferation to bacteria resistant to antibiotic treatment.

The FDA is allowing 30 days for filing comments on the proposal and for expected requests for a hearing by pharmaceutical firms and other affected commercial and agricultural interests. The FDA spokesman said a final ruling on penicillin - which could be challenged in the courts, while sales continue - may be a year away.