President Bush's nominee to head the Environmental Protection Agency (search) ran into more problems Monday in the Senate as a third Democrat, presidential aspirant John Edwards, said he would join efforts to block the nomination.

Democrats Sens. Hillary Rodham Clinton of New York and Joe Lieberman of Connecticut, who also is seeking the presidential nomination, previously had said they would put a hold on the nomination of Utah Gov. Mike Leavitt (search) as EPA administrator.

Edwards of North Carolina said Monday the nomination should not go forward until the Bush administration provides detailed information on how human health will be affected by changes the administration wants in the way the EPA regulates air pollution, especially from power plants.

The Democrats have accused the administration of rolling back protections under the Clean Air Act (search) by easing pollution control requirements on power plant operators and industrial plants.

Clinton, who was the first to say she would block Leavitt's nomination, said she would not allow it to go forward until the administration responds more fully to a report that the EPA misled New Yorkers about the health risks from contaminated air in the aftermath of the World Trade Center terrorist attacks.

An EPA inspector general said he EPA, at White House request, provided misleading advisories about the potential risks. Administration officials have denied any intention to mislead.

Any senator can put a hold on a nomination, preventing it from being scheduled for a floor vote. Traditionally Senate leaders, no matter which party, have abided by such a request, although a nomination may still go through the committee process.

A hearing by the Environment and Public Works Committee on Leavitt's nomination was expected to be held as scheduled this Thursday. Sen. James Inhofe, the panel's chairman, said he planned to go ahead with a committee vote on the nomination shortly, despite the holds that have been placed.

Bush announced his selection of Leavitt, a Republican known for seeking consensus on environmental issues and avoiding confrontation, on Aug. 11 to succeed Christie Whitman as head of the EPA.

While Leavitt's selection has been criticized by environmentalists, the opposition in the Senate appeared to be less a reaction to the former Utah governor than to the Bush administration's environmental policies in general, particularly related to issues involving air quality.

"I've put a hold on the nomination to try to get the EPA to tell the truth about the safety of the air we breathe," said Edwards in a statement. He said that more than a year ago he and 43 other senators asked the EPA to conduct "a rigorous analysis" of the public health effects of administration proposals on clean air rules.

When Lieberman on Sept. 6 announced his support for Clinton's decision to block the Leavitt nomination, he said it was in part because of "this practice of stonewalling" by the administration on information about its environmental rules as well as information surrounding the health risks after the Sept. 11, 2001, World Trade Center attack.

The White House said it regretted that Leavitt's nomination was being held up, accusing Democrats of attempt to "politicize" the issue, despite Leavitt's qualifications.

On Monday, Bush renewed his call for changing the way power plants would have to meet air pollution requirements. His "Clear Skies" initiative would ease regulatory controls on utilities and establish a broader market-based system for getting reductions in smokestack emissions.

Bush also defended changes in EPA regulations that will allow power plants to make improvements to produce more electricity -- and more pollution -- without adding additional, costly air pollution controls.