The Environmental Protection Agency says groundwater has been contaminated by pesticides in parts of 38 states, but it cautions that more study is needed before the full extent of such pollution can be determined.

The agency said Tuesday a review of 150 groundwater studies over the past 10 years found 74 different chemicals in 38 states. Similar findings had been announced by advocacy groups using EPA documents obtained under the Freedom of Information Act.The EPA has added new information. It said that farming has put 46 chemicals in the groundwater of 26 states and 32 chemicals got into groundwater in 12 states because of "point source" pollution, such as an accidental spill.

Unknown sources account for 28 chemicals in 12 states, not necessarily the same 12 involved in point-source contamination.

"There are dangers" in trying to draw national conclusions from the data, which are "not appropriate for assessing human exposure," said Victor Kimm, the agency's acting assistant administrator in charge of pesticides.

"Many agricultural areas have not been sampled and are not statistically represented," he said.

The studies sampled shallow sampling wells and aquifers used for irrigation in addition to drinking water.

The agency said concentrations generally were below its "health advisory" levels for drinking water, but some were not.

EPA is in the process of sampling 1,300 drinking water wells nationwide to check for 125 different chemicals according to a statistically based scheme that should yield national conclusions in late 1989 or early 1990.

The studies responsible for Tuesday's findings were conducted by government agencies, universities and holders of pesticide licenses, and EPA said it was still interviewing the authors to check the validity of their work.

Diane Baxter, staff scientist of the National Coalition Against the Misuse of Pesticides, said that she was not surprised by EPA's findings. "This is the tip of the iceberg. As more samples are taken, we are going to find more instances of contamination."

John McCarthy, vice president for science and regulatory affairs at the National Agricultural Chemicals Association, a pesticide manufacturers' trade group, agreed that the results were not appropriate for assessing human exposure, and said "EPA's current sampling is the kind of information we will look to as to whether there's a health issue."

Until 1979, pesticides had been thought not to get into groundwater; it was thought that they remained bound to soil. Since then, concern has risen as more and more contamination has been found.

When EPA announced a proposed pesticides-in-groundwater strategy in February, it said it knew of 19 pesticides from farming in the groundwater of 24 states.