The Reagan administration did not adequately study the protections needed formigratory wildlife before adopting a plan last year for offshore oil and gas leasing through 1992, a federal appeals court ruled Friday.

The U.S. Circuit Court of Appeals said the Interior Department "failed to perform an adequate analysis of the cumulative impacts of the program on migratoryspecies." It ordered the department to try again, though the ruling does not immediately impede the leasing program.The wildlife at issue include the gray whale and salmon that migrate in the north Pacific between California and Alaska, and various migratory birds.

The appeals court's unsigned, 64-page opinion rejected all other aspects of a challenge against the five-year plan adopted by Interior Secretary Donald P. Hodel in July 1987.

The previous five-year plan survived all court challenges.

The latest plan was challenged by the National Resources Defense Council, other environmental groups and the states of California, Massachusetts, Oregon and Washington.

Leasing activities have not been held in abeyance pending the legal fight, however, and are not immediately affected by Friday's ruling. The appeals court ordered the Interior Department to comply with federal environmental law by providing the required environmental impact statements on migratory species.

"This is a significant victory for the environment," said James Thornton of the National Resources Defense Council in San Francisco. "It allows the new secretary of interior and (President-elect) Bush to look at the entire leasing program and decide whether there should be a kinder, gentler five-year plan."

He said the ruling would carry a profound impact for federal waters off northern California, Oregon and Washington where as yet no oil and gas leasing has occurred.

The American Petroleum Institute, the largest trade group, said it was pleased with the decision: "It reaffirms what we have long been saying, that the five-year offshore leasing program does address adequately and fairly the concerns of state and local interests."