The business group that went to court to make Congress clean up its act proclaimed a victory yesterday and announced that new pollution control gear finally will be installed on the power plant that heats and cools the halls of Congress.

Under an agreement in the Environmental Protection Agency, the Capitol power plant has promised to comply with the Clean Air Act by 1982 -- a total of 12 years after the law was passed, said James Richards, legal director of the Capital Legal Foundation.

Accusing Congress of violating the only law it ever specifically promised to obey, the foundation filed a law suit last year charging the plant was violating the air pollution standards set by the District of Columbia under the federal law.

Richards said at the time he was "trying to teach Congress an object lesson" by demanding that congressional smoke stacks meet the same emission standards as those of the businesses that back his foundation.

Federal agencies are exempt from virtually all government regulations, Richards explained, but when Congress passed the Clean Air Act in 1970, the lawmakers decreed that federal installations would have to stop polluting.

The foundations's lawsuit charged that the architect of the Capitol plant -- the federal official responsible for the plant -- had defied District efforts to enforce the law, refusing to accept a notice of violation from local officials and telling power plant operators they were to pollute the air at night only, when no one would notice.

Tests this year of emmissions from the smoke stack at New Jersey Ave. and E Street SE, showed the Capitol power plant was putting out from two to four times the pollutants permitted by D.C. standards. After the tests, the Capitol architect signed an agreement with the EPA to install new pollution gear, and that produced a settlement in the lawsuit.

George M. White, the architect of the Capitol, said yesterday his department will spend between $500,000 and $1 million on new pollution gear for the congressional boiler room.

"We're not doing anything we wouldn't be doing anyway," White said. "We always planned on complying with the law."

Congress already has appropriated money for pollution control equipment on the plant, White said, but it hasn't been installed because his agency was too busy building an addition to its cooling plant and because "the technology [for controlling pollution] keeps changing."

Richards offered no sympathy. "If this had been a private facility, they would have been fined," he said.

Pooh-poohing the role of the Epa in the case, Richards said the federal pollution-fighters "studiously ignored the problem until we went to court." The D.C. Department of Air and Water Quality tried to control foul air on the Hill, he added, but got no help from higher-ups in city government in taking on the congressional polluters.

Nor did environmental groups offer to aid in the lawsuit, added Richards, whose foundation frequently opposes environmentalists in cases over enforcement of pollution laws.

He admitted the foundation was "practicing a little symbolism" in the case. "One of the things we're interested in is showing that the government, which makes the laws, has to live with them, just like the rest of us."