WASHINGTON — A $537 million, decade-long study ordered by Congress concluded Thursday that acid rain should be “viewed as a long-term problem” requiring pollution controls but is not the environmental crisis some scientists have suggested.

The report by the National Acid Precipitation Assessment Program was embraced both by those who support steep cuts in sulfur dioxide emissions and by critics of such cuts. The critics have long claimed that severe pollution controls, costing as much as $5 billion a year, are an overreaction to the acid rain problem.

In its final draft report, the scientific group, known as NAPAP, reiterated that pollution-control measures are needed to return hundreds of lakes and streams — especially in the Northeast and the mid-Atlantic states — to healthy conditions.

The report also acknowledged that acid rain is affecting visibility across much of the East; causes damage to some forests, particularly red spruce at higher elevations; reduces soil nutrients; kills some aquatic life; erodes buildings and statues, and poses health problems to some humans exposed to acidic aerosols.

James Mahoney, director of NAPA, outlined the draft report to a final meeting of the group and said its findings have “reduced the scientific uncertainties” about acid rain.

“Acid rain is correctly viewed as a long-term problem which should be resolved by permanent measures,” he concluded, summarizing the findings.

Mahoney said that while the study supports many of the scientific views expressed over the years on acid rain it also rejected other “more extreme views” such as those that consider it “a flat-out crisis” or those “who would say there’s no problem at all.”

NAPAP was established by Congress in 1980 to improve the understanding of acid rain. During its decade of work it spent $537 million.

The most severe pollution control requirements would have to be imposed on electric utilities, especially those burning high-sulfur coal in the Midwest, for the results to be effective, the study said.

The National Coal Association issued a statement urging that Congress ease its acid rain pollution controls in light of the NAPAP study. “The report provides strong evidence that there is time to implement more cost-effective ways in which to mitigate the limited environmental impacts of acid rain,” said Richard Lawson, the association’s president.

But Eileen Claussen, a senior director involved with air pollution issues at the EPA, said the NAPAP report “clearly establishes the link between (sulfur) emissions and environmental damage.