The Environmental Protection Agency issued draft regulations yesterday that would ease long-standing pollution controls on older, dirtier power plants by judging these plants by the hourly rate of emissions rather than the total annual output.

EPA Administrator Stephen L. Johnson said the administration is confident its recent efforts to curb harmful nitrogen oxide and sulfur dioxide pollution by establishing a separate cap-and-trade system will do more to clean the air than the New Source Review rule the agency seeks to modify.

"We're focused on practical, achievable results that don't get delayed by years of litigation," Johnson said in a telephone news conference. "Let me be clear: This is not about getting rid of New Source Review. This is about making it work better."

But environmentalists and some of EPA's own lawyers said the move will undermine one of the agency's most effective means of forcing aging utilities to install new anti-pollution technology when they expand or modernize. Under the current law, a plant must put in new controls if a modification increases its annual emissions; the new rules would require such controls only if the hourly emissions increase. Under the new scenario, a plant could legally emit more pollution if it operated for longer hours.

"Whatever shell of New Source Review remained, it's now being completely eviscerated," said John Stanton, a senior attorney at the advocacy group Clear the Air.

Although New Source Review has existed since 1977, the government started aggressively pursuing violators under the Clinton administration, and the Bush administration has continued to prosecute many of those cases. Some officials fear the rule change will undermine at least a dozen lawsuits against 50 utilities that are still in court.

An Aug. 25 memo from EPA's air enforcement division director, Adam M. Kushner, obtained by The Washington Post from the Natural Resources Defense Council, an environmentalist group, warns "the proposed rule will adversely impact our enforcement cases and is largely unenforceable as written." Kushner also wrote that, "as written, NSR would never be triggered" for dirty power plants.

Granta Nakayama, assistant administrator for EPA's Office of Enforcement and Compliance Assurance, said yesterday that the question of whether the rule change will undermine current cases "is something we're looking at." He added that the administration will continue to press its current lawsuits but will pursue only the utilities that violate the new standards.

NRDC clean-air director John Walke said because one of the administration's proposals is tied up in court and the new rules have yet to take effect, Nakayama's statement means that "the administration's going to let utilities get away with violating the laws on the books. It's astonishing."

Industry officials echoed the administration, saying the change does not mean they are no longer required to clean up aging facilities.

"From an air quality perspective, it is important to understand that the U.S. electric power sector is legally obligated to continue significantly reducing emissions, regardless of any changes to the New Source Review program," said Edison Electric Institute spokesman Dan Riedinger, who represents utilities producing half of the nation's electricity. "There's nothing wrong with a vigorous and honest debate about NSR reform, but allegations that changing the program will lead to more pollution represent a gross distortion of the facts."

But Emily Figdor, a clean-air advocate at U.S. PIRG, said changing the rule could cause 70,000 additional premature deaths by 2025, because power plants will not have to adopt as strict pollution controls as they would under existing law.

EPA spokeswoman Eryn Witcher disputed that analysis, saying "the new air programs put in place under the Bush administration get us 70 percent air pollution reductions that 10 years of power plant enforcement haven't come close to doing."

Bill Wehrum, assistant administrator for EPA's air and radiation office, said the 70 percent pollution reductions will take full effect sometime after 2020.

Johnson said the agency would take 60 days of public comment before finalizing the new rules.

The administration may face a legal challenge, however. Peter H. Lehner, bureau chief in the New York Attorney General's Environmental Protection Bureau, said his office will challenge it in court.