The Washington area's $1 billion effort to clean up the Potomac River has failed to meet its goal, led to more than $120 million in wasted funds and needlessly added millions of dollars more to homeowners' sewer bills, the General Accounting Office said yesterday.

The decade-long cleanup drive "cost much more than necessary and accomplished much less than expected," the federal watchdog agency concluded in a comprehensive 159-page study. It accused regional governments of incurring "excessive costs in unsuccessfully attempting to develop and implement pollution abatement programs and facilites."

GAO said its "case study" of failures in the Potomac antipollution campaign raised nationwide issues, which it urged Congress to address when it considers revisions of the Federal Water Pollution Control Act in coming months. The new GAO report is expected to figure in congressional debate on the 1972 law.

The GAO study contrasts markedly with other recent reports citing substantial gains in the Potomac's water quality over the past decade, and it prompted pointed objections from some local and federal officials.

A report drafted for the Environmental Protection Agency by a consulting firm last year hailed the Potomac cleanup drive as "A Decade of Progress" and said water quality near the Woodrow Wilson Bridge, a once heavily polluted area, had "significantly improved." It found about a 50 percent decrease in phosphorous, a 35 percent drop in oxygen-demanding substances, a 10 percent increase in dissolved oxygen and other beneficial changes.

The new GAO study does not dispute such findings. Instead, it questions whether the money used to achieve this progress was properly spent and expressed doubt that additional expenditures will bring about significant enough benefits to justify the costs.

"Because the same obstacles which have caused past planning efforts to fail are as formidable as ever, current planning efforts for D.C. area waste water treatment and sludge disposal facilities to help clean the Potomac have little chance of success," the report said.

Efforts to clean the Potomac have drawn national attention since former President Lyndon Johnson called for making the river "a conservation model for our metropolitan areas" in his 1965 State of the Union message. So far, GAO said, the Washington area has spent or obligated itself to spend $1.05 billion, including $769.7 million in U.S. funds, to plan and build water treatment plants to stem Potomac pollution.

As evidence of misspending, GAO said that $123 million has been allocated to designing facilities that never were built or constructing facilities that are not needed or are minimally used. A prime example, the agency says, was the Anacostia force main, a federally financed, $67 million pipeline intended to carry sewage to the Blue Plains waste treatment plant. The force main proved unnecessary, GAO said, partly because Blue Plains lacks capacity to handle the additional sewage.

GAO said another $5.3 million was spent on studies that yielded "no acceptable recommendations."

The GAO found that Washington-area residents may be needlessly responsible for $35 million in composting projects. It said these plants may have been eligible for federal grants covering 75 percent to 85 percent of their costs, but that regional governments failed to meet requirements to obtain the federal aid.

Many of these assertions were disputed by regional officials.

GAO attributes the Potomac's problems largely to a tangled history of political battles and court conflicts among county, city and federal officials that have failed to resolve two key issues -- where to build additional waste treatment plants and where to dispose of the mounting volumes of sludge, a semisolid waste residue. It accuses regional governments of "paralysis by analysis" -- postponing decisions by resorting to continual studies.

Among key recommendations to Congress, GAO urged giving regional water quality agencies more authority to carry out, rather than merely propose, plans for solving water pollution disputes.

A congressional aide with expertise in water quality issues said yesterday that Congress is likely to consider such a move, though it may prove too controversial. Another approach, the aide said, may be to increase the authority of state governments over water quality issues.