The head of the Environmental Protection Agency said Tuesday he didn't know of behind-the-scenes efforts by EPA officials to blunt state attempts to reduce mercury emissions from power plants.

Those efforts occurred even as the Bush administration argued in court that states are free to enact tougher mercury controls from power plants, The Associated Press reported last month, based on internal EPA documents.

Sen. Patrick Leahy, D-Vt., questioned EPA Administrator Stephen L. Johnson about the report at a hearing of the Senate Appropriations environment subcommittee.

"Has anyone with EPA ever pressured any state against instituting any more restrictive mercury regulation?" asked Leahy, who chairs the Senate Judiciary Committee.

"I don't recall having any firsthand knowledge of that," said Johnson. "I don't know if they have, no I don't," he added.

Leahy cautioned Johnson that such pressure on states was inappropriate, and if it did occur, "then the EPA gave misleading information to the courts, which is an extremely serious matter."

A federal appeals court last month struck down the Bush administration's industry-friendly approach for mercury reduction that allowed plants with excessive smokestack emissions to buy pollution rights from other plants that foul the air less.

Internal EPA documents obtained by the advocacy group Environmental Defense show attempts over the past two years to bar state efforts to make their plants drastically cut mercury pollution instead of trading for credits that would let them continue it.

Many states did not want their power plants to be able to buy their way out of having to reduce mercury pollution.

The push to rein in uncooperative states continued until the eve of the Feb. 8 decision by the U.S. Court of Appeals for the District of Columbia Circuit that struck down the EPA's program. A day before that ruling, the White House Office of Management and Budget approved a draft regulation to impose a "federal implementation plan" for mercury reduction in states whose mercury control measures did not meet EPA approval.