he Food and Drug Administration, long focused on judging the effectiveness and safety of drugs in the body, is considering requiring more tests for their possible effects on the environment, agency officials said yesterday.

The officials said the environmental side of the drug-approval process, which was cut back in 1997, will probably be re-evaluated in light of a federal survey of streams that found traces of a host of medications, excreted by people and livestock, that were not captured by sewage treatment plants.

"We're looking very carefully at this data and aren't ruling out the fact that we may have to make changes," said Dr. Steven K. Galson, deputy director of the F.D.A. Center for Drug Evaluation and Research.

The survey of more than 100 waterways downstream from treatment plants and animal feedlots in 30 states found minute amounts of dozens of antibiotics, hormones, pain relievers, cough suppressants, disinfectants and other products. It is not known whether they are harmful to plants, animals or people.

The findings were released yesterday on the Web site of the United States Geological Survey (http:// toxics.usgs.gov), which conducted the research, and in an online journal, Environmental Science and Technology.

Additional federal studies are under way to see if any contamination reaches taps or ground water used for drinking, but the program under which they are conducted, the toxic substances hydrology program of the geological survey, is slated to be eliminated under budget cuts proposed by the Bush administration, government officials said.

The $14-million-a-year program was created in the Reagan administration, and its data are used by many state agencies and federal scientists. The Bush administration has instead proposed providing $10 million a year to the National Science Foundation for water quality studies.

Federal officials, drug company scientists and private environmental campaigners all said yesterday that the Geological Survey program provided the first comprehensive concrete data on levels of antibiotics, hormones and other drugs in American waterways.

Many of these substances fall through regulatory cracks because they are not defined as pollution under clean-water laws, and they are not all checked for environmental effects by the food and drug agency.

In 1997, the F.D.A. followed Clinton administration efforts to streamline many regulations and greatly reduced the number of drugs for which environmental assessments were required. A review of hundreds of previous drug assessments turned up no instances where the compounds, once out of the body, had an adverse effect, agency officials said.

Some categories were excluded from such assessments, including hormones, like estrogen, which are natural substances.

"They streamlined the process so much that it's virtually nonexistent for a lot of drugs," said Dr. Rebecca Goldburg, a senior scientist at Environmental Defense, a private lobbying and research group.

Now, however, estrogens and similar compounds are increasingly the focus of research by the Environmental Protection Agency and many scientists because of hints that they alter sexual characteristics in fish and other aquatic species.

"As we look more at low levels of drugs, it appears that some of them have real biological effects in real situations," Dr. Goldburg said.

About 40 percent of the streams in the study showed traces of estrogen or other reproductive hormones.

Some drug company scientists said that one hurdle to assessing the effect of hormones — like those in birth control pills — is that the substances are also naturally produced by people, wild animals and some plants.

"It's hard to see what we'd be able to do about that," said Dr. James R. Hagan, the vice president of Glaxo SmithKline for corporate health, environment and safety.

"It's one thing to regulate the things we add to the environment," Dr. Hagan said. "But some of these things have been there as long as there have been various plants around."

An even bigger challenge, he and many scientists said, will be to get a clear sense of whether there are risks posed by the dilute mixtures of many substances that are not captured by water treatment methods.

Dr. Galson of the F.D.A. said that measuring minute amounts of the substances in many streams was just one of many steps toward determining whether they pose a risk to people or wildlife.

"There's still a lot of work to do," he said.