The District's Blue Plains sewage treatment plant is accused of improperly dumping raw sewage into the Potomac River in a suit filed yesterday by the Environmental Protection Agency.

The federal suit against the District government alleges that the plant also violated pollution-control regulations by dumping chlorinated water into the river. And the suit alleges that the city did not complete construction of two water treatment projects it promised to build.

The area's largest treatment plant, Blue Plains handles 70 percent of the sewage in the region. Arlington, Fairfax, Loudoun, Montgomery and Prince George's counties pay the District to treat their sewage.

"They aren't properly operating and maintaining the plant, which can have catastrophic consequences, including failure of the plant," said Daniel Palmer, a lawyer in the Environmental Protection Agency's Office of Enforcement and Compliance Monitoring. "That's what this is all about, trying to prevent a catastrophic breakdown."

EPA has counted 375 violations since February 1989, with each violation having a potential penalty of $25,000, exposing the city to fines of more than $9.3 million, according to the EPA's regional office in Philadelphia.

The District government issued a statement saying officials had not had a chance to review the suit but would respond appropriately.

"The Blue Plains Wastewater Treatment Plant provides one of the most advanced waste water treatment processes in the country and as a result has made dramatic improvements to the quality of the environment and the Potomac River," said Tara Hamilton, spokeswoman for the D.C. Department of Public Works. "At this time, we are meeting all effluent requirements of the permit and intend to continue to do so."

Discharging raw sewage without disinfecting it means that bacterial and viral agents remain when it goes into the river, which is used by communities downstream as a source of drinking water after it is treated. The release of chlorinated water could be toxic to fish, such as rockfish, he said.

In 1985 the District agreed to make extensive improvements at the plant, which it has failed to do, the EPA said yesterday. The plant also is under investigation for alleged cost overruns and unnecessary spending.

The EPA, trying to show it is cracking down on polluters of the Chesapeake Bay, released a list of 56 administrative actions yesterday that it and states around the bay had taken against businesses, governments and one individual during the last quarter. Penalties assessed or collected against the polluters exceed $3.7 million, the agency said.

Of those polluters, 19 were publicly owned or government-operated waste water treatment plants or hazardous material disposal facilities in Virginia, Maryland and Pennsylvania. They include facilities in Arlington and Prince Frederick counties and in Poolesville.

In May, the EPA and federal prosecutors won their largest financial penalty ever against an individual violator. Paul Tudor Jones II, a multimillionaire and Wall Street commodities trader, was fined

$1 million and ordered to pay another $1 million in restitution after he pleaded guilty in federal court to damaging ecologically sensitive wetlands on his 3,272-acre private hunting retreat on Maryland's Eastern Shore.