WASHINGTON  Federal food regulators took a tentative step Monday toward banning a common use of penicillin and tetracycline in the water and feed given cattle, chickens and pigs in hopes of slowing the growing scourge of killer bacteria.

But the Food and Drug Administration has tried without success for more than three decades to ban such uses. In the past, Congress has stepped in at the urging of agricultural interests and stopped the agency from acting.

In the battle between public health and agriculture, the guys with the cowboy hats generally win.

The F.D.A. released a policy document stating that agricultural uses of antibiotics should be limited to assuring animal health, and that veterinarians should be involved in the drugs’ uses.

While doing nothing to change the present oversight of antibiotics, the document is the first signal in years that the agency intends to rejoin the battle to crack down on agricultural uses of antibiotics that many infectious disease experts oppose.