The United States, alone among major western nations, has adopted policies that may worsen the problem of acid rain, according to a new study released yesterday by the Environmental Law Institute.

Gregory Wetstone, an official of the nonpartisan research institute who is co-author of the report, said the study suggests that the United States "has retreated from its historic leadership position" at a time when international environmental issues are of increasing importance.

"The precedent established in response to today's comparatively straightforward acid rain issue will set the tone for crucial efforts to head off these and other international environmental problems in coming years," Wetstone said.

The report said that the U.S. government has approved changes in state emission controls that will allow pollution sources to release an additional million tons of sulfur dioxide annually, thus becoming the only western industrial nation to take a step backward, rather than forward.

Sulfur dioxide and other pollutants are changed chemically in the atmosphere, and come to earth as acid rain, which has been blamed for killing aquatic life in thousands of lakes in Scandinavia, Canada and the northeastern United States.

Wetstone noted that West Germany, which long resisted entreaties from the Scandinavian countries to curb its emissions, recently decided to cut back sulfur dioxide emissions.

Wetstone and his colleague, Armin Rosencranz, also found a positive sign in indications from British officials that future energy and pollution control policies will take transboundary concerns into account.

The report is likely to fuel debate between the United States and Canada, which attributes much of its acid rain damage to sulfur dioxide emissions from the United States.