Despite more than a quarter century of efforts by some lawmakers and regulators to force the federal government to police the oil and gas industry, politics have repeatedly caused U.S. EPA studies to be narrowed in scope and important findings to be removed.

Now, some scientists and lawyers at the agency are wondering whether history will repeat itself as EPA undertakes a broad new study of the potential risks of natural gas drilling, the preliminary results of which are set to be delivered next year.

Already, documents show EPA has dropped plans to study radioactivity in drilling water that is discharged by treatment plants into rivers upstream from drinking water intake plants.

And last year, the agency had planned to call for a moratorium on hydraulic fracturing in the New York City watershed, internal documents indicate, but the advice was removed from the publicly released letter.

One agency scientists who was involved in the writing said this could be explained with one word: "politics."

As it stands, natural gas drilling companies have major exemptions from parts of at least seven of the 15 federal environmental laws that govern most other heavy industries.

For example, coal mine operators have to get permission from federal authorities before injecting toxic wastewater into the ground. But natural gas companies do not have to follow the same rules when they want to inject chemical-laced water and sand into the ground during hydrofracking.

And regulators add together the air pollution coming from a steel plant's various buildings when they decide whether certain strict rules will apply. But the toxic fumes coming from a natural gas site's components -- a compressor station, a storage tank, for example -- are counted separately, meaning many overall gas well operators get looser caps on their emissions.

Now, with the new study of hydraulic fracturing looming, internal EPA documents show that topics included in earlier versions of the research plan -- for instance, the dangers of toxic fumes released during drilling -- have been cut.

Research into how drilling waste affects the food chain and the risk of radioactive waste to workers were also dropped, documents show.

Several agency scientists and consultants, who declined to be named for fear of reprisals, said the study was narrowed because of pressure from industry and its allies in Congress, as well as time and budgetary limits.

Brendan Gilfillan, an EPA spokesman, said the plan remains broad and that the agency has taken additional steps to investigate the effects of drilling, including issuing a subpoena against the energy services company Halliburton Co. to force fuller disclosure about its drilling operations.

But federal scientists say the national study is being used to cut other research by EPA on hydrofracking. At a January meeting, Jeanne Briskin of EPA's Office of Research and Development told regional directors that the national study would be the only forum for research on hydrofracking (Ian Urbina, New York Times, March. 3). -- AS