By Ian Talley, Of DOW JONES NEWSWIRES

WASHINGTON -(Dow Jones)- Republican lawmakers are demanding an investigation into claims that the Environmental Protection Agency suppressed a staff-prepared study that argues against the agency's proposal that greenhouse gases are a danger to public health.

Besides asking for an Inspector General investigation, lawmakers are also asking the agency to re-open the controversial rulemaking to allow inclusion of the study.

The Competitive Enterprise Institute, or CEI, last week released an 85-page scientific study authored by two EPA staff that undercuts the agency's " endangerment" decision, as well as several emails that show the agency rejected inclusion of the report in its rulemaking process.

The CEI accused EPA management of suppressing the work of senior EPA economist Alan Carlin and EPA environmental scientist John Davidson "for political reasons."

Senator James Inhofe, R-Okla., ranking member of the Senate Environment and Public Works Committee, Rep. Darrell Issa, R-Calif., ranking member of the House Oversight Committee, and Sen. John Thune, R-S.D., are now grilling the agency over why the study wasn't originally included.

EPA Press Secretary Adora Andy said Carlin's "general views on the subject of climate change" were "heard and considered inside and outside the EPA and presented at conferences and at an agency seminar."

"The claims that his opinions were not considered or studied are entirely false," Andy said in a statement.

CEI, which calls itself a "public interest group dedicated to free enterprise and limited government," opposes the Obama administration's efforts to regulate greenhouse gases.

The Endangerment proposal is one step in the rulemaking process that paves the way for regulation of greenhouse gases such as carbon dioxide. Congress, meanwhile, is moving forward with its own regulatory approach based on the assumption that greenhouse gases are a danger to the public.

"I am concerned about the credibility of the Obama administration's arguments in favor of increased environmental activism and government regulation now that it is clear that legitimate differences of opinion are not tolerated within the EPA," Sen. Thune said.

Matthew Dempsey, a spokesman for Sen. Inhofe, said his boss was probing the matter with the agency because of the seriousness of the charges.

"This is an administration that promised an 'unprecedented' level of transparency and accountability, yet, it is actively seeking to withhold new data in order to justify a political conclusion," Rep. Issa said. "The American people deserve to know all the facts, not have their information filtered or censored based on what is politically convenient for the administration," he said.

The CEI said the emails reveal a political agenda.

"The administrator and the administration has decided to move forward on endangerment and your comments do not help the legal or policy case for this decision," Al McGartland, director of the National Center for Environmental Economics, told Carlin in a March 17 email released by CEI. McGartland said another reason not to include Carlin's study is because "this is not a criteria document for climate change and greenhouse gases."

Carlin's comments, he said, would cause a "very negative impact on our office." Carlin said he didn't provide his emails to the CEI.

Referring to Carlin, EPA spokeswoman Andy said "certain opinions were expressed by an individual who is not a scientist and was not part of the working group dealing with this issue."

Still, Carlin was allowed to make general presentations on climate change " inside and outside the EPA and presented at conferences and at an agency seminar," Andy said.

Further, Carlin was allowed to join a committee that organizes an ongoing climate seminar series. The study was largely written by Carlin, but also includes work by EPA environmental scientist John Davidson.

Carlin and Davidson have been with the agency since its inaugural years in the early 1970s. Carlin holds a doctorate in economics from Massachusetts Institute of Technology and a bachelor's degree in physics from California Institute of Technology, Pasadena, Calif. He has published a raft of papers in recent years examining climate change regulatory systems in journals such as the Environmental Law and Policy Review. Davidson holds a doctorate in physics from the University of Michigan.

According a March 16 email, two-thirds of Carlin's study referenced peer- review publications. The remainder referenced "significant new research" since the publishing of the United Nations's Intergovernmental Panel on Climate Change last report, a seminal document that the U.S. government is using as a foundation for its climate policies.

The references to the new studies, he says, "are significant because they present information critical to the justification (or lack thereof) for the proposed endangerment finding," Carlin said in the email.

The EPA late last week allowed Carlin to publish the study on his personal Web site.

After repeatedly trying to circulate the comments in early March to the Office of Air and Radiation, the primary division responsible for drafting the endangerment proposal, Carlin was told his study would not be included, according to the emails.

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