A federal appeals court panel yesterday ordered the Environmental Protection Agency to decide speedily whether to subject strip mines to clean air regulations because of dirt that is thrown into the air during excavation.

The Clean Air Act, as the EPA interprets it, requires the agency to regulate facilities that emit at least 250 tons of small particles a year. According to an EPA document quoted in the ruling, a small strip mine would generate 1,750 tons of dust and dirt particles, including 175 to 262 tons that are small enough to be inhaled and cause respiratory problems.

However, the EPA has not included strip mines on the list of facilities it plans to regulate under the Clean Air Act, and contends that it is still studying the matter.

"If there is reasoned decision-making lurking behind such agency behavior, it is yet to be articulated," D.C. Circuit Court Senior Judge David Bazelon wrote in a strongly-worded opinion in Sierra Club v. Anne M. Gorsuch (former EPA administrator).

In a 2-to-1 ruling, the court pointed out that the EPA has been deliberating the strip mining issue since 1979, and "in the meantime, fugitive emissions from new strip mines" have gone unregulated. Bazelon called the omission of strip mines from the list of regulated facilities "troubling."

The ruling by Bazelon and Circuit Court Judge Ruth Bader Ginsberg, with Senior Judge George E. MacKinnon dissenting, gives the EPA 90 days to decide whether to regulate strip mines. In an unusual twist, Bazelon wrote that the court will retain jurisdiction over the case as EPA deliberates and will review the agency's decision to determine whether it is "arbitrary and capricious."

The EPA, joined by 10 mining companies and one mining organization that intervened on the agency's side, had argued that the circuit court had no power to rule on the matter since the EPA was still in the process of making a decision. However, the ruling implies that the agency's failure to decide was in effect a decision not to regulate them.

The EPA and 10 mining companies and a mining organization that intervened on the agency's side argued there is not enough data to prove whether strip mine particles are covered by the Clean Air Act. But Bazelon said the EPA had placed other facilities on the list despite incomplete data.