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In one of the emails released by Mr. Vitter, former EPA Region 8 Administrator James Martin advised the Environmental Defense Fund about where hearings on EPA rules for greenhouse gases should be held for maximum effect.

Mr. Martin said holding the hearing in Denver “will make Roy Palmer nervous” — apparently a reference to Xcel Energy Inc.’s senior vice president for public policy.

Mr. Martin has not responded to two email requests for comment.

The requests were made at a time when Mr. Obama is trying to get a new EPA administrator confirmed by the Senate, and the two matters are getting intertwined.

House Science Committee Chairman Lamar Smith, Texas Republican, sent a letter Tuesday to the EPA asking for several emails involving Ms. McCarthy.

Mr. Smith said in his letter that he is trying to figure out how the EPA uses science to back up the rules and regulations it issues.

Mr. Obama nominated Ms. McCarthy last week.

She currently is the assistant administrator in charge of air and radiation.