Guidelines issued to animal drug makers by the Food and Drug Administration are intended to address concerns that animal antibiotics are being passed to humans through food, possibly allowing harmful bacteria to develop immunity to drug treatment.

The proposal outlined by the FDA on Wednesday suggests procedures drug manufacturers could use to determine whether new animal antibiotics would contribute to the escalating problem of drug-resistant bacteria.

The agency said humans are most likely exposed to resistant bacteria through animals produced for food. Environmental groups said the statement shows the agency is acknowledging that animal antibiotics are overused and are a health risk.

FDA spokesman Larry Bachorik said the agency isn't making conclusions, but wants to assess whether using drugs on farm animals is a health risk to humans.

Farmers have been criticized by environmental and health groups for feeding antibiotics to animals, even when they aren't sick. The animal drug industry argues that using antibiotics on farm animals actually makes food safer.

Karen Florini, a spokeswoman for Keep Antibiotics Working, said the draft is a sign that federal regulators are recognizing antibiotics are overused in farming. But she said the agency is failing to address the problem that farmers are using large quantities of the drugs.

"The elephant in the room is the vast quantity of antibiotics already being administered to farm animals,'' said Florini, who also works for Environmental Defense.

The Animal Health Institute, a group representing drug manufacturers, said the draft merely provides manufacturers with an outline of risks to consider when seeking approval of new drugs.

"The concept of risk assessment is a far better tool than legislative bans, which is what some groups have proposed,'' said Ronald Phillips, a spokesman for the industry group.

Sen. Edward Kennedy, D-Mass., and Rep. Sherrod Brown, D-Ohio, have proposed legislation that would restrict the use of some antibiotics for animal use. Florini said the proposal will likely be discussed next year.

The FDA is seeking comments from the public on its proposed guidelines.