In that study, which began in the mid-1970s, scientists signed confidentiality agreements so they could track the private medical and occupational histories of more than 22,000 individuals in six cities around the country. They combined that personal data with home air-quality data in order to study the link between chronic exposure to air pollution and mortality.

Academics aren’t typically required to turn over such private data when submitting studies for peer review by other specialists in the field, or for review and publication in scientific journals, which is the traditional way that this kind of research is evaluated. If academics were to turn over the raw data to be made available for public review, the agency would have to spend hundreds of millions of dollars, according to a federal estimate , to redact private information.

The bottom line, critics say, is that if the E.P.A. is limited to considering only studies in which the data is publicly available, the agency will have a narrower and incomplete body of research to draw on when considering regulations. “It sends a pretty chilling message to scientists that their work can’t be used or won’t be used,” said Sean Gallagher, a government relations officer with the American Association for the Advancement of Science, a nonprofit science advocacy organization .

Mr. Pruitt laid out his plans for the new transparency policy in an interview last week with The Daily Caller, a conservative news site. The proposal is based on legislation named the Honest and Open New E.P.A. Science Treatment Act, also known as the Honest Act, a bill sponsored by Representative Lamar Smith, a Texas Republican. The bill has failed to gain support in Congress for years despite having the support of the energy, manufacturing and chemical industries.

That legislation aimed to preclude the E.P.A. from using any studies that could not be independently reproduced. According to data compiled by the Center for Responsive Politics , a nonpartisan research group that tracks campaign finance data, versions of the bill have received support from Exxon Mobil, Peabody Energy, Koch Industries and the American Chemistry Council, which provides policy and research for major chemical companies including Arkema, DuPont and Monsanto.

Mr. Smith, the sponsor of the stalled Congressional legislation, applauded the E.P.A.’s proposed move. “Our citizens have a right to see the data that the E.P.A. says justifies their regulations,” he said in a statement. He has argued that E.P.A. regulations in the past were justified by data that was impossible to verify independently.