The District of Columbia has sued the Environmental Protection Agency, Maryland and a group of Suburban developers in an effort to halt the opening of a sewage treatment plant that would discharge effluent into Rock Creek Park.

"The park is special," District counsel John Salyer said. "We can't let it be tampered with."

The plant, built in Rockville by a consortium of private developers who plan to turn it over to the Washington Suburban Sanitary Commission, would discharge up to 3 million gallons of effluent daily into Rock Creek. During the summer dry season, effluent generally would exceed the normal flow of water in the creek, which empties into the Potomac River between Foggy Bottom and Georgetown.

In its suit, filed in U.S. District Court, the city said the effluent "will cause a reduction in quality . . . of Rock Creek" and that the plant would be able "to discharge totally untreated sewage into Rock Creek in emergencies . . ."

Maryland officials, however, claim that the effluent would be cleaner than the normal flow of the creek "in a good number of parameters," including coliform count and turbidity. Coliform count (a measurement of human and animal waste) is used to determine whether a body of water is safe for human contact. Turbidity means clarity.

Maryland officials also noted that the first 15 miles of Rock Creek below the plant are in Montgomery County. "We are not going to do anything that would adversely impact the creek," Montgomery County environmental planner David Sobes said.

The District's Salyer said he did not think the suit would affect the city and Montgomery County's decision last year to collaborate on a regional sewage treatment solution built around construction of a big sewage treatment facility at Dickerson in upper Montgomery.