More than 130 million gallons of raw or partially treated sewage have illegally overflowed from Washington Suburban Sanitary Commission pipes into the waterways, streets and basements of suburban Maryland over the past two years, according to agency records.

The sewage pollutes the Anacostia and Patuxent rivers with human waste and puts nearby residents at increased risk of such life-threatening diseases as cholera and infectious hepatitis, according to the federal government and environmental groups. They said better maintenance of aging pipes could have prevented overflows at the water and sewage utility, which serves 1.6 million residents of Montgomery and Prince George's counties.

WSSC officials blamed the volume of overflows on unusually severe storms, such as Hurricane Isabel last year, and said they are taking steps to address the situation.

"This is a large problem," said Jon Capacasa, the Environmental Protection Agency's director of water protection for mid-Atlantic states. WSSC, he said, is "running into failure mode."

Overflows are a problem for utilities across the country. Between 23,000 and 75,000 occur nationwide every year, resulting in the release of 3 billion to 10 billion gallons of untreated wastewater, according to EPA estimates.

EPA officials and several outside experts declined to characterize the severity of overflows at WSSC in comparison with problems at other utilities, citing scant national data and the unique environmental and structural factors in each system.

Nevertheless, EPA Assistant Administrator Benjamin Grumbles said, "130 million gallons discharged is 130 million gallons too much. It's a violation of the Clean Water Act and EPA policy."

For the past two years, the EPA has been negotiating an enforcement agreement to legally require the utility to improve its 5,300-mile system of pipes. Capacasa said he expects it to be finalized within the next few months.

Three environmental groups -- the Natural Resources Defense Council, Anacostia Watershed Society and Audubon Naturalist Society -- said they plan to file a lawsuit against WSSC by the end of the month to force the utility to stop the overflows.

WSSC spokesman Chuck Brown said the utility is implementing measures to prevent the problem. The agency plans to spend $85.8 million over the next six years to replace old pipes and analyze overflow patterns, he said, more than twice the $40 million spent on those programs from 1996 to 2001. The utility also formed a group last year to maintain sewer lines, Brown said.

"We are working to prevent and minimize [overflows] wherever possible," he said. "But we can do more, and we will do more."

Environmental groups, however, said the utility has inadequately addressed the problem.

"I think every sewage system in the country is saying, 'Sure, we're working on it.' But the question is, are they doing enough?" asked Nancy Stoner, director of the Natural Resources Defense Council's Clean Water Project. "As far as we've seen, WSSC does not have the critical pieces in place to solve the problem."

Brown said the volume of overflows is due mainly to weather patterns over the past two years.

Of the 126.4 million gallons of sewage that overflowed last year, 106 million occurred during Hurricane Isabel, according to utility records.

EPA officials said heavy storms are usually when the most severe overflows happen. Rainwater seeps into the sewer pipes, causing raw sewage from the overloaded system to gush into such waterways as the Anacostia and Patuxent rivers; back up into basements of businesses and homes; and spill out of manholes into streets.

Older systems, called combined sewer systems, convey stormwater and untreated sewage together and are designed to dump the mix into waterways during heavy rain. WSSC has a more modern sanitary system in which wastewater and sewage are carried in separate pipes.

"Those type of sewer systems are not designed to overflow," Capacasa said. "If they are adequately maintained, operated and invested in, they should not overflow with any frequency."

This year, 4.4 million gallons have overflowed on 97 occasions, according to utility records. During heavy rain over the Fourth of July weekend, 3 million gallons of sewage entered the Anacostia and tributaries.

The Anacostia Watershed Society said WSSC overflows are responsible for much of the pollution in the Anacostia. Fecal coliform bacteria levels are much higher in the Maryland portion of the river than in the District, according to sampling data from the group. Robert E. Boone, president of the Anacostia Watershed Society, said those high levels strongly suggest that WSSC pipes are polluting the waterway.

"This is the 21st century," he said. "It's time we stop putting human sewage in the river."

The EPA's enforcement action against WSSC is the most recent of a dozen similar high-profile settlements with utilities across the country. In 2002, Baltimore agreed to pay a $600,000 fine and make more than $900 million in sewer repairs as part of a settlement with the EPA. Last year, the D.C. Water and Sewer Authority said it would pay a $250,000 fine and make $150 million in improvements.

But environmental groups said legal actions, such as the one against WSSC, are necessary only because the Bush administration has not strengthened measures to curb sanitary sewer overflows. During the final days of the Clinton administration, the EPA proposed a rule that would have tightened regulations of sanitary systems. But the Bush administration shelved the proposal after taking office.

Environmentalists said the withdrawal of the rule left the nation's 19,000 sanitary sewer systems without a guide to end the overflows.

"This situation with WSSC is a good example of why we need regulations that were shelved by the Bush administration," Stoner said. The withdrawn proposal would have required utilities to implement plans to reduce overflows and monitor sewage discharges. It would also have required utilities to notify the public and health authorities whenever sewage overflowed into streets or waterways.

"There should be a sign that says 'There is sewage flowing in this street. You might want to avoid it,' " Stoner said. "It's common sense."

Utility industry officials objected to the proposed rule because of its estimated annual cost of $93.5 million to $126.5 million. They also said it is impossible to eliminate sanitary sewer overflows.

"The rule was impractical," said Adam Krantz, a spokesman for the Association of Metropolitan Sewerage Agencies. "There has to be more flexibility, because there are limited funds to deal with this problem."

Grumbles said the EPA might eventually propose a modified version of the rule, although he said it is considering whether a focus on enforcement might be more effective than further regulation. He also said that the agency is "strongly encouraging" all utilities to address the overflows.

Stoner said enforcement is a significantly slower way to combat the problem than comprehensive regulation. The EPA can do only "half a dozen cases a year now to bring communities into compliance," she said. "Take that versus the thousands that would have been affected by this rule."