Frustrated by the Bush administration's air pollution policies, Democratic Sen. Thomas Carper (search) plans to block the Senate from confirming President Bush's nominee to become administrator of the Environmental Protection Agency (search).

The Delaware senator is "going to place a hold on the nomination of Stephen Johnson (search) to be head of the EPA," Carper's spokesman, Bill Ghent, said Thursday. All senators have the power to hold up the confirmation of a nominee.

The White House had no immediate comment.

Carper has complained about what he describes as stonewalling by the White House and EPA over data requested during the past several years on various legislative proposals aimed at cutting pollution from power plants.

At a meeting Wednesday of the Senate Environment and Public Works Committee (search), Carper was the lone senator to vote against Johnson. The committee voted 17-1 to advance his nomination to the full Senate.

Carper said he believed Johnson, a career EPA employee for about 25 years and the first person with a science background to be nominated the lead the agency, would be "a very good administrator" — if the White House didn't interfere with him politically.

"I believe if Steve Johnson is to be an effective administrator, he needs to be unfettered by this administration," Carper said. "To get the right legislation, we need to get good, timely technical data."

After the meeting, Carper said EPA and other federal agencies traditionally provide unbiased scientific information on legislation whenever Congress asks for it.

"But for the last four years, the EPA has been constrained from providing us with unfettered and timely information about legislative and regulatory proposals, especially those having to deal with air pollution," he said.

The committee chairman, Sen. James Inhofe, R-Okla., said he hoped to move the nomination to the Senate floor as soon as possible.

"It is a testament to Steve's hard work in public service that he has been nominated to lead the EPA and I expect strong bipartisan support for him from the full Senate," Inhofe said Wednesday.

Johnson, who currently serves as EPA's acting administrator, was nominated in March to succeed Mike Leavitt, who left in January to lead the Health and Human Services Department.

Last week, Johnson's decision to meet Democrats' demands and cancel plans for a controversial study using children in Duval County, Fla., to measure the effect of pesticides cleared the way for the committee vote on his nomination.

Sens. Barbara Boxer, D-Calif., and Bill Nelson, D-Fla., had demanded that the two-year study be canceled. Boxer voted for Johnson, she said she had "great reservations."

"I'm going to go with my hopes, not my fears," she said.