A federal appeals court blocked the EPA on May 14 from imposing tougher air quality requirements that the agency says are needed to protect children and people with respiratory problems.

The 2-1 ruling on a lawsuit by a number of industry groups was a major defeat for the Clinton administration, which has viewed the air regulations as one of its top environmental accomplishments.

The EPA said it intends to appeal the decision, and has instructed states to move forward with pollution control plans that meet its July 1997 standards, which dramatically reduced the amount of ground-level ozone —or smog — and microscopic soot allowed in the air.

The court decision is of concern to the Bay because meeting the new standards requires cuts in nitrogen oxide emissions, which are also a major source of nitrogen entering the Bay.

But most of the actions EPA has taken so far to control smog, such as its move last fall ordering 22 states to curb NOx emissions, were needed to meet the old ozone standard, and likely would be unaffected by the court ruling. Last fall’s action alone is expected to keep about 8 million pounds of nitrogen a year out of the Bay.

EPA officials also said the decision would not affect the need for the new tailpipe emission standards announced in May.

In its ruling, the U.S. Court of Appeals for the District of Columbia rejected claims by the industry groups that the regulations were based on incomplete and poor science and were too costly. But two of the three judges concluded the EPA failed to justify the pollution levels it selected as minimum requirements to protect public health.

The agency “construed [sections of] the Clean Air Act so loosely as to render them unconstitutional delegations of legislative power,” wrote Judges Douglas H. Ginsburg and Stephen F. Williams.

Judge David S. Tatel, who joined the other two judges in some of the decision, nevertheless, issued a strong dissent on this key point. The EPA, in fact, used “reasonable explanations” for setting the standards it chose, he wrote.

The EPA has argued that current ozone and soot standards do not protect certain segments of the population, including small children, the elderly and people with respiratory ailments.

The revised air standards limited ozone, an essential part of smog, to 0.08 parts per million averaged over 8 hours, instead of 0.12 parts per million averaged over 1 hour under the old requirement. And for the first time, they required that states regulate microscopic particulates, or soot, from power plants, cars and other sources down to 2.5 microns, or 28 times smaller than the width of a human hair.

EPA Administrator Carol Browner called the court ruling “bizarre” and “illogical” — and a total surprise to the agency. “It seems to fly in the face of more than a half a century of U.S. Supreme Court rulings,” she said. “The decision is illogical. It would have you believe that in 1990, Congress and the Bush administration … perpetuated a cruel hoax by on the one hand directing EPA to strengthen air quality standards, and then, with the other hand, gutting the EPA’s powers to enforce these standards.”

Industry representatives and critics of the regulations in Congress quickly applauded the decision. “It's a big victory, one of the biggest,” said Robin Conrad, senior vice president for litigation at the U.S. Chamber of Commerce. She said the ruling acknowledged industry’s claim that the EPA in setting the standard was “picking numbers out of the hat.”

— The Associated Press contributed to this report