Carper's move came after Johnson, now acting EPA administrator and a career agency scientist, refused to commit his agency to study legislative alternatives to the administration's plan to cut utility air emissions through a cap-and-trade system.

Johnson last week responded to a similar threat from Sen. Barbara Boxer of California by canceling a program to test pesticides on Florida infants.

Carper said the White House has restrained the EPA from doing objective scientific analysis of his proposal to reduce utility pollution.

"For the life of me I don't understand the reluctance of the administration to do that," he said. "I've repeatedly been denied an analysis of my proposal, presumably because the White House is afraid of what it might show."

An EPA spokesman referred queries on Carper's objections to the White House. A White House spokeswoman referred questions to the administration's Council on Environmental Quality. A spokeswoman for the council was not available.

Carper said Johnson late Wednesday told him "he's not in a position to provide the information at this point and time."

Johnson said he is reluctant to commit EPA staff to the study -- which would take about 10 weeks -- without the approval of Senate Environment Committee Chairman James Inhofe, Carper said.

Inhofe tried to pass a version of the administration's plan in his committee, but the panel deadlocked over the speed of emission cuts and Republicans' decision to exclude action on heat-trapping carbon dioxide.

"Senator Carper has more information about the multi-pollutant legislation then Congress ever has," an Inhofe spokesman said, referring to 10,000 pages of documents the EPA has produced to the committee.

"We hope that the obstruction of a nominee of his caliber and bipartisan support will not continue," Inhofe's spokesman said.