Financially pressed governments in the Washington area should relax environmental goals regulating discharge from sewage treatment plants into the Potomac River to save hundreds of millions of dollars, according to a controversial report released yesterday by the Greater Washington Research Center.

The blue-ribbon panel also urged the District of Columbia government to increase its water and sewer rates to discourage excessive water use and save millions. The report urged a sliding scale -- like those already used in most suburban jurisdictions -- that would impose higher rates for heavy users than for those who consume water sparingly. It did not propose specific fees. A District official said later that such a plan is already under consideration.

The proposal for scaling back sewage-treatment goals was immediately attacked by national and regional environmental groups. Officials of the Chesapeake Bay Foundation, Clean Water Action Project and Friends of the Earth contended that the move would likely increase pollution in the Potomac and the bay.

"It's the height of folly," said William C. Baker, executive director of the Chesapeake Bay Foundation.

The report was the latest in a series of studies issued by the nonprofit research center's task force on local government, headed by former World Bank president Robert S. McNamara. A separate report last week sparked controversy by warning that Washington-area governments will face $605.3 million in revenue shortages by fiscal 1987. Officials said yesterday that the proposed sewer and water savings were aimed at helping to close this gap.

The waste-treatment cutbacks would save $25 million to $50 million a year in operating expenses and hundreds of millions of dollars in long-term spending for construction of treatment plants and other capital expenditures, task force officials said.

At a briefing on the report, William G. Colman, a task force member and former executive director of the Advisory Commission on Intergovernmental Relations, argued that the proposals "would have no significant detrimental effect" on the Potomac or the Chesapeake Bay.

A preliminary study by the Metropolitan Washington Council of Governments, a regional planning agency, has already suggested that some relaxation of sewage-treatment goals may be possible without jeopardizing the Potomac. An official of the Environmental Protection Agency, which regulates waste-discharge requirements, said yesterday that an easing of standards may be permissible.

At issue were goals set by EPA for discharges from the Blue Plains and other area sewage-treatment plants. The plants currently comply with some of these targets but fail to meet others. Officials recommended yesterday that the plants continue to comply with the standards that they have already met, but be granted federal approval to avoid meeting the remaining unmet targets.

William Johnson, the D.C. environmental services director, said yesterday that his agency is already studying a "tiered rate system" that would be aimed at deterring excessive water consumption by setting higher charges for heavy use.

The District's water and sewer rates are now the lowest in the metropolitan area, he said. The Fairfax County Water Authority and the Washington Suburban Sanitary Commission, which serves Montgomery and Prince George's counties, have higher rates for heavy users than light users.