WASHINGTON (AP) _ The Environmental Protection Agency relied on ''solely political reasons'' to reject a staff recommendation that some oil and gas drilling wastes be more strictly regulated, an agency employee says.

''Politics overrode science and we've never done that before,'' said Hugh Kaufman, assistant to the EPA's director of the hazardous site control division.

''This is the first time in the history of environmental regulation of hazardous wastes that the EPA has exempted a powerful industry from regulation for solely political reasons, despite a scientific determination of the hazardousness of the wastes,'' he said in an interview.

Kaufman and another staff member, who spoke on condition of anonymity, said Sens. Lloyd Bentsen, D-Texas, Phil Gramm, R-Texas, and Don Nickles, R-Okla., pressured the agency, as did the Interior and Energy departments and some states.

EPA administrators deny their call was swayed by political pressure.

The majority of an EPA working group that studied the issue had recommended that a small volume of drilling wastes come under stringent regulation as hazardous.

But EPA Administrator Lee Thomas and J. Winston Porter, EPA's assistant administrator for solid waste and emergency response, said in a June 30 report to Congress they had decided that all oil and gas drilling wastes would remain exempt from hazardous waste rules.

Porter said it was ''certainly a close call ... not an easy decision,'' but that his ''conscience is clear.''

So-called ''associated wastes'' account for 1 percent of the total volume of drilling wastes but contain highly toxic materials such as benzene, heavy metals and corrosive acids that are regulated as hazardous in other industries, the EPA staff said. It concluded the wastes pose a threat to the environment if not handled properly and that states are largely doing a poor job of enforcing existing regulations.

A draft staff report said the cost to the industry to regulate those materials as hazardous wastes would have ranged from $200 million to $500 million a year.

''However, relative to total production and the total volume of product, the overall impacts on the industry should not be unduly burdensome,'' the report said.

''It would have been a fly in the economic health of that industry,'' said Kaufman, a frequent public critic of top-level agency decisions. Kaufman and officials responding to his accusations spoke in interviews last week.

Porter agreed with the staff position that many states do not adequately regulate drilling wastes, but said another layer of regulation was not the answer. Hazardous waste laws can be inflexible and are not necessarily appropriate for the nation's hundreds of thousands of oil and gas wells, he said.

Porter wrote Thomas that although the working group had wanted to regulate the low-volume wastes as hazardous, ''we now feel that removing any portion of the exemption would be too disruptive and burdensome to both the regulated industry and the regulating agencies.''

Gramm spokesman Larry Neal said the costs would have posed a huge economic burden on an industry staggered by three years of low prices. Of the senator's push against the regulations, Neal said: ''If we'd do it again tomorrow, we'd do it just as strong.''

Bentsen, tapped by Democratic presidential candidate Michael Dukakis to be his running mate, said the EPA's decision was ''by and large sound, though there are some areas that may require further clarification and explanation.''

Nickles said additional regulations would have hurt people ''already on their backs economically'' and that states are doing a decent job.