The Clinton administration told the owners of 392 power plants and other facilities yesterday to cut nearly in half their output of a smog-inducing chemical, a new tack in an ongoing campaign to reduce the pollution that wafts state to state.

Many states, particularly in the Northeast, have argued they cannot meet federal air quality standards without help in tackling pollution originating beyond their borders. Last year the Environmental Protection Agency labeled 22 states as sources of cross-boundary chemicals and ordered deep cuts in emissions.

That effort has bogged down in litigation, and yesterday the EPA bypassed the states and, for the first time, directly targeted specific sources of pollution. It ordered a 49 percent reduction in nitrogen oxide emanating from 277 power plants and 115 other facilities in the District and 12 states, including Virginia and Maryland. Combined with sunlight and other pollutants, nitrogen oxide produces smog, which aggravates asthma and other health problems.

"One way or another, we're going to get there, we're going to get people clean air," EPA Administrator Carol M. Browner said during a telephone news conference. Browner estimated that the agency's directive will improve air quality for 100 million citizens, both in states downwind from pollution sources and in those where sources are located.

Meeting the EPA's order to cut nitrogen oxide by 510,000 tons annually by 2003 will cost the affected businesses about $950 million each year, the agency estimated, and could increase the average utility bill by 1.2 percent. Deregulation of the industry, however, should offset that rise, officials said.

EPA officials said the 392 facilities are largely in compliance with laws governing emissions. But because states downwind are still experiencing problems, the facilities must do still better, the officials said. "What we're establishing today is a new legal requirement," said one, who asked not to be identified.

David Flannery, legal counsel for the Midwest Ozone Group, said the utility association "certainly will" file suit to block the EPA's action because it requires all the plants to reduce emissions to the same level, regardless of their current impact on air quality.

"And we'd hope Ms. Browner is no more successful in the litigation over this issue than she has been in the previous litigation," said Flannery, whose group is involved in the court case stemming from the EPA order last year aimed at the 22 states.

Pat Hemlepp, spokesman for American Electric Power, an Ohio-based company that is one of the nation's largest utilities, described the latest order as "just another of the many collaborative efforts between the agency and Northeast states to target Midwest sources." That effort, Hemlepp said, ignores the real source of most pollution: emissions by cars, trucks and buses locally.

Environmentalists, however, applauded the EPA's step. Rebecca Stanfield, of the U.S. Public Interest Research Group, said that even if less sweeping than the effort directed at the 22 states, "it will make a significant difference." And Frank O'Donnell, executive director of the Clean Air Trust, said that although the new order is "more limited," it is "clearly going to mean cleaner air."

Technically, the EPA's action began with petitions filed by four states--Connecticut, Massachusetts, New York and Pennsylvania--that asked the EPA to protect them from pollution generated elsewhere, a request they are entitled to make under federal law. Similar petitions are pending from Delaware, Maryland, New Jersey and the District, but EPA officials said that if granted, the effect will not be great, because air quality in the four remaining petitioner-states will improve because of yesterday's action.