WASHINGTON — The Food and Drug Administration today called on drug companies to help limit the use of antibiotics given to farm animals, a decades-old practice that scientists say has contributed to a surge in dangerous, drug-resistant bacteria.

Antibiotics are mixed with animal feed to help livestock, pigs and chickens put on weight and stay healthy in crowded barns. Scientists have warned that this leads to the growth of antibiotic-resistant germs that can be passed to humans.

The FDA has struggled for decades with how to tackle the problem because the powerful agriculture industry says the drugs are a key part of meat production.

Under the new FDA guidelines, the agency recommends antibiotics be used “judiciously,” or only when necessary to keep animals healthy. The agency also wants to require a veterinarian to prescribe the drugs. They can currently be purchased over-the-counter by farmers.

“Now you have a veterinarian who will be consulting and providing advice to these producers, and we feel that is an important element to assure that they are in fact using these drugs appropriately,” said William Flynn, a deputy director in FDA’s veterinary medicine center.

The draft recommendations by the FDA are not binding, and the agency is asking for drug manufacturers’ cooperation to put the limits in place.