A federal appeals court panel, rejecting arguments from the mining and electric industries, ruled unanimously yesterday that the Environmental Protection Agency was correct in adding mining sites and fly-ash pits to its priority list for "Superfund" cleanup.

The decision, issued by the U.S. Court of Appeals here, held that the EPA was acting "fully within its power" when it decided that mining wastes and fly ash, a byproduct of coal-burning, were "hazardous substances."

The ruling, while a clear victory for the government, comes as the Reagan administration is pushing for legislative changes that would sharply restrict Superfund cleanups of most mining sites.

According to EPA officials, the agency now believes that strip-mine law should be used to clean up mining wastes. The EPA also has argued that allowing Superfund cleanups of mining wastes unfairly penalizes the petroleum and chemical industries, which pay most of the taxes that finance Superfund.

Before it had that change of heart, however, the EPA put several mining sites on the Superfund list, including the massive Tar Creek site, which straddles the Oklahoma-Kansas border, where toxic seepage has contaminated streams and ground water. The agency also listed a Chisman Creek, Va., site where Virginia Power has deposited fly ash.

The court consolidated those cases and six others in its ruling. Judge Kenneth Starr, writing for the three-judge panel, said that Superfund's legislative history was murky on the question of mining wastes and fly ash, but that the law itself was clear and EPA's interpretation of it was reasonable.

The opinion opens the way for adding more mining sites to the Superfund list. The administration has argued that the Surface Mining Control and Reclamation Act should apply to those sites, although an EPA official said yesterday that its proposed changes in the Superfund law would "not preclude us from using Superfund."

Some members of Congress have been skeptical of the proposal, however, noting that the strip-mining law has been ensnarled in controversy since its passage in 1977. An aide to Rep. James J. Florio (D-N.J.) said yesterday that the law's limited cleanup fund might not be adequate to deal with lead, copper and zinc mines as well as the coal mines it was intended to regulate.