A Commonwealth Court judge ruled yesterday that Pennsylvania's rule limiting mercury emissions from power plants was "unlawful, invalid and unenforceable."

Environmentalists criticized the decision, saying it denied the state's children protection from toxic mercury pollution.

But a spokesman for PPL Generation L.L.C., the Allentown utility that filed suit against the state, said the company was pleased to get "clarity" about regulations.

The U.S. Environmental Protection Agency originally passed regulations that a federal court overturned, ordering the EPA to write new ones. Last week, the new EPA administration issued a memo saying it would. But Pennsylvania elected not to participate in the federal program and passed stricter regulations.

PPL has invested $1.5 billion in control technology at its two Pennsylvania plants, said spokesman George Lewis. The state's rules would have required additional "tens of millions, perhaps hundreds of millions," of dollars.

He said PPL did not want to move forward "only to find that the new EPA rule said, 'Nope. That's the wrong technology. We're ordering you to install something else.' "

Jan Jarrett, president of Citizens for Pennsylvania's Future, which in 2004 filed a petition on behalf of many groups demanding state regulation, blamed "the Bush administration's failed and ill-advised regulatory charade" for yesterday's ruling.

Invalidating the state rule because the Bush regulations were nixed by the federal courts, she said, "brings a new and ironic twist to the saying 'throwing the baby out with the bath water.' "

John Hanger, acting secretary of the state Department of Environmental Protection, said the ruling makes Pennsylvania's economy "less competitive in the long run." He said the agency would "carefully consider our legal options."