Stephen Johnson (search), President Bush's nominee to head the Environmental Protection Agency (search), won overwhelming approval Wednesday from a Senate committee -- but still could have his confirmation blocked by a Senate Democrat.

Johnson, the acting EPA administrator, cleared the way last week for Wednesday's committee vote by agreeing to Democrats' demands that he cancel plans for a controversial study using children to measure the effect of pesticides.

By a 17-1 vote, the Senate Environment and Public Works Committee sent Johnson's nomination to the full Senate for consideration. But the lone dissenter, Sen. Thomas Carper (search), D-Del., said the Bush administration was still blocking his requested studies on how to cut pollution from power plants.

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

After the hearing, Carper's spokesman, Bill Ghent, confirmed the senator was seriously considering whether to block a Senate vote on Johnson's nomination, by using the power all senators have to hold up the confirmation of a nominee. Carper hoped to speak with Johnson later Wednesday.

"He's keeping his options open as far as blocking the nomination," Ghent said.

Sens. Barbara Boxer, D-Calif., and Bill Nelson, D-Fla., had demanded the cancellation of the pesticide study. Over the study's two years, EPA had planned to give $970 plus a camcorder and children's clothes to each of the families of 60 children in Duval County, Fla., in what critics of the study noted was a low-income minority neighborhood.

Boxer said she voted for Johnson despite misgivings on a number of EPA policies.

"I am still very troubled by the EPA's direction on human test studies," she said. "I have great reservations about Johnson's nomination, but I'm going to go with my hopes, not my fears."

Johnson has been a career EPA employee for about 25 years and is the first person with a science background to be nominated the lead the agency. Johnson would succeed Mike Leavitt, who left the agency in January to become head of the Health and Human Services Department.