A coalition of civic activists and environmental groups filed suit yesterday to halt the biggest District highway project in more than two decades, accusing the government of covering up the presence of hazardous waste along the route.

The federal court suit against city and federal officials is a last-ditch attempt to stop the $200 million Barney Circle Connector, which will link Kenilworth Avenue and the Southeast-Southwest Freeway. City officials say construction will begin in a few weeks and will take about three years.

The road will include a four-lane bridge over the Anacostia River that would be the city's first new automobile crossing since the 11th Street Bridge opened in 1970.

The road's supporters -- including Mayor Sharon Pratt Kelly, federal highway officials and some Capitol Hill residents -- say it will take thousands of cars off streets by providing a quicker way to jockey between Interstate 395 and Route 295. Federal funds will pay 90 percent of the cost, and when Kelly endorsed the road in September she said the project would provide thousands of jobs.

But civic groups, the Committee of 100 and environmental organizations contend the road is a dinosaur that will bring more pollution, traffic and noise to city neighborhoods, pave 20 acres of parkland and dirty the Anacostia River.

Their suit also raised the issue of "environmental justice," saying the freeway would benefit Maryland commuters and more affluent Capitol Hill residents while hurting largely African American neighborhoods in Southeast Washington.

Federal officials studied the road's environmental effect in 1983, but the lawsuit said they should take a second look to account for subsequent discovery of lead-contaminated soil and the combined pollution from the road and a proposed theme park on nearby Children's Island.

City officials suspected soil contamination in 1991 and had test results to confirm it in 1992, according to documents obtained by the plaintiffs under the Freedom of Information Act. Lead was found on the west bank of the Anacostia River. City officials did not disclose the problem during two public hearings last summer.

The pollution, which probably came from incinerator ash in an old landfill, may require excavation of up to 59,000 tons of dirt, enough to cover a football field 24 feet deep, according to city studies. Exposure to lead, even at low levels, can cause brain damage in children.

"Would you want hazardous waste in your front yard?" asked Eleanor Hill, of the Barney Circle Neighborhood Watch. She was among two dozen civic and environmental leaders at a news conference announcing the lawsuit. "We are angry because there was no intention to tell the neighbors."

City officials said 59,000 tons is a worst-case figure and contended the waste poses more hazards now, seeping into the groundwater, than if excavated and removed. They said they will release a full report on the extent of contamination and how to get rid of it within a few weeks.

City officials heard of a "potential problem" two years ago but "we didn't know the full extent of it until recently," said Gary Burch, the city's chief transportation engineer. "We're not trying to hide anything."

The road proposal has split the city's political leadership. Council members John Ray (D-At Large), Hilda H.M. Mason (D-At Large) and Bill P. Lightfoot (I-At Large) have demanded a new environmental impact statement, and Ray sent a representative to yesterday's news conference to underline his opposition to the freeway. Council member Harold Brazil (D-Ward 6), whose district includes the road, issued a statement yesterday saying that he favors "some further environmental study," but he did not go into more detail.

Yesterday's lawsuit, filed by the Sierra Club Legal Defense Fund on behalf of eight environmental and civic groups, could be the first of two over the road project.

Three additional groups -- the D.C. Federation of Civic Associations, the Audubon Naturalist Society and the Citizens Committee to Stop It Again -- plan to sue if the city does not satisfy their doubts that officials did not consider all the alternatives to the freeway project, according to lawyer Roberts B. Owen.

Critics say those alternatives could include expanded highway ramps or "traffic management" steps such as making more streets one-way.