WASHINGTON – The Environmental Protection Agency said Thursday it anticipates it will delay by three months, until next March, putting in place new controls for reducing mercury emissions from power plants.

Already under a court order to act by mid-December, the agency said it has accepted the offer of an extension by the environmental group that had sued to force the new controls. Both sides expect approval from the U.S. Court of Appeals for the District of Columbia Circuit for the additional time.

The Natural Resources Defense Council said it hoped the EPA uses the time to thoroughly analyze its assumptions behind the rules.

“We will do what analysis is needed to make sure a proper decision is made,” the agency’s administrator, Mike Leavitt, told reporters in a telephone conference call.

Leavitt previously has promised to re-examine a plan that envisions a 70 percent cut in mercury emissions from coal-burning power plants by 2018.

Mercury is a toxic substance that can cause neurological and developmental problems, particularly in children. Once in the environment, it remains an active toxin for thousands of years.

Leavitt said the delay would give the public more time to offer opinions because the comment period is being extended by 60 days beyond Friday’s deadline.

He said agency officials welcomed the extension because they want “all the available data” to help develop the first regulations of mercury from power plants in “an evenhanded and proper way, utilizing the best available facts.”

John Walke, clean air director for the council, urged the EPA to toughen its controls.

“They’re too weak and too slow to protect the public. So we hope they’ll take the time to do their job this time, and adopt timely, protective mercury controls,” Walke said.

The group sued the government in 1992, contending the EPA failed to determine which utility emissions are hazardous air pollutants and did not decide whether to regulate them. The suit was settled in 1994, then modified in 1998 to set deadlines for action on specific pollutants.

Mercury releases from power plants are not regulated now. The substance settles in waterways and accumulates in fish. The Food and Drug Administration has warned that high levels of mercury in some fish, including albacore tuna, can pose a hazard for children and for pregnant or nursing women.

Earlier this month, 45 senators, including seven Republicans, and attorneys general from 10 states, mostly in the Northeast, urged the EPA to propose stronger requirements.

The Clinton administration had offered a proposal that envisioned cutting mercury emissions by 90 percent by 2008. That would have required utilities to install the best available technology and prohibited the trading of pollution credits.

The Bush administration scrapped those plans and proposed regulating mercury in a way similar to smog-causing nitrogen oxide, acid rain from sulfur dioxide and other pollutants. That meant setting nationwide limits on pollution below current levels, and letting plants unable to reduce their share pay for cuts by other plants that do more than required. It also wanted to give utilities longer to comply and reduced the target to 70 percent.

Utilities argued they could not meet the 90 percent reduction or 2008 deadline.