ASHINGTON, March 13 - The Bush administration this week will propose the first federal controls on mercury emissions from coal-fired power plants. The new rule will abandon the Environmental Protection Agency's original tilt toward a remedy favored by most environmental groups in favor of a system of tradable pollution allowances that is more congenial to industry.
The new E.P.A. rule is intended to cut emissions to 38 tons, a 21 percent reduction from 1999 levels, in 2010 and to as little as 15 tons, or about a 69 percent reduction, in 2018, according to the draft of the final rule sent to Bush administration budget officials this weekend for final vetting.
Under the rule, some utilities will be able to buy allowances rather than cleaning up emissions. Environmentalists and some state officials have argued that this approach will lead to so-called hot spots posing significant risks to local populations. The administration has tended to favor trading of pollution allowances as a regulatory tool that it believes is both effective and less prone to legal challenge, pointing to the success of such a program in curbing the pollution that causes acid rain.
The rule is certain to infuriate some environmental groups that have long called for stringent mercury regulation and argued that mercury was too great a health hazard to be an appropriate candidate for market-based regulation that, by its nature, results in uneven enforcement and protects some populations more than others.
Mercury, a commonplace of everyday life a generation ago found in home thermometers and school science labs, has in the past two decades been found to cause direct harm to the development of nervous systems in infants and young children. Infants have been exposed before birth to mercury consumed by their mothers, studies have shown.
The most common form of exposure is believed to be the consumption of fish - including tuna and swordfish - in which the metal has accumulated.
But agency officials point out that much of the mercury exposure of the United States population is out of reach of any federal regulation. Much airborne mercury deposited in the United States originates abroad, and most of the mercury-laden fish consumed by Americans as fish sticks or fish fillets is imported.
As expected, the new rule provides the last piece of a regulatory plan that in many ways mimics the blueprint laid out in the Bush administration's stalled Clear Skies legislation and accomplishes many of the legislation's goals for establishing market-based policies as a primary component in environmental regulation.
Accompanying the rule will be a document reversing the agency's formal conclusion of December 2000 that it was "appropriate and necessary" to require utilities to scrub as much mercury as possible from coal-fired power plants.
The long-awaited provision, which is officially named the Clean Air Mercury Rule, is expected to be released Tuesday. It is intended to work in tandem with an E.P.A. rule published last Thursday, which controls two chemicals that are building blocks for soot and ground-level ozone. The agency maintains that controls mandated under this Clean Air Interstate Rule will have the "co-benefit" of reducing mercury emissions to the levels set for 2010.
A draft of the proposed rule, dated March 10, was provided to The New York Times by a government official uncomfortable with the process the agency used to arrive at its conclusion. It differs somewhat from an analysis recently criticized by the E.P.A.'s inspector general as a rigged attempt to support a predetermined conclusion. But the latest version does not address the inspector general's criticisms that alternatives were not thoroughly studied.
From 1990 to 1999, total airborne emissions of mercury in the United States dropped from 209.6 tons to 113.2 tons, roughly 5 percent of worldwide manmade emissions. Mercury emissions from power plants are responsible for about 48 of the 113 tons. Even though large reductions in mercury emissions from municipal and medical waste incinerators and chemical factories have been achieved over the past decade, at least 44 states have issued advisories calling for limited consumption of fish from mercury-contaminated streams.
The rule would have limited effect on canned tuna, the single greatest contributor, per capita, to mercury in the diet of United States residents.
Contacted about the rule, Cynthia Bergman, a spokeswoman for the E.P.A., said on Sunday that it would make the United States "the first country in the world to regulate emissions from coal-fired power plants." Ms. Bergman added that the agency in the 1990's took "big steps" to regulate emissions from other sources, like municipal incinerators.
Felice Stadler, a mercury policy specialist at the National Wildlife Federation, was sharply critical when told on Sunday of the thrust of the new rule, saying that it was "the weakest air-toxics rule ever written for a major industry" by the E.P.A.
"This rule gives big energy companies an extra 10 years before being required to reduce their mercury air pollution," Ms. Stadler said. "To say we are disappointed is an understatement. This is an ill-conceived plan that puts the future of our children and natural places at risk."
The new rule, like the Clean Air Interstate rule that it complements, will set up a cap-and-trade system of negotiable pollution allowances that is administered by the states, each of which has its own mandated cap on emissions and each of which can develop its own system of distributing allowances, subject to the approval of the environmental agency.
Authority and responsibility for meeting these standards is given to the states, whose annual caps between 2010 and 2017 range from a high of 4.7 tons in Texas to lows of zero emissions in Idaho and Vermont.
Some states, like Connecticut, already regulate power plant emissions of mercury. The new federal rule will not impede their ability to impose stricter controls than those mandated by the E.P.A.