The 70-acre marsh next to the Kenilworth Aquatic Gardens, once a lush wetland swarming with fish and other wildlife, now resembles a brown desert at low tide.

Silt and pollution killed most water plants, fish and animals in the marsh years ago, turning it into a virtual mudflat. Still, a few osprey, beavers and herons hang on.

"There's still a lot of critters out there, but it's not the way it used to be," explained Steve Syphax of the National Park Service, which owns the marsh.

Now the Kenilworth marsh is the focus of an ambitious experimental replanting project that is part of a larger campaign to restore the health of the Anacostia River. The multimillion-dollar effort involves Maryland, the District, the federal government and regional planning organizations. Now nearing the end of its second year, it aims to turn the river around by the turn of the century.

Private groups also are getting involved. A group of business leaders and conservationists called START, for Stop Trashing the Anacostia River Today, announced a fund-raising campaign this spring to help clean up the river and turn its banks into a "continuous grand river park" from the District into Prince George's County.

Unlike the successful drive to bring back the Potomac River, which largely depended on upgrading the Blue Plains sewage plant, efforts to restore the Anacostia involve a variety of projects, from stream cleanups and marsh replantings to storm drain improvements. Many of the projects cost only a few thousand dollars.

From Bladensburg to Buzzard Point, the Anacostia was once a heathy river and rich fishery, but over the years it has become choked by sediment from local construction, streambank erosion, and the sand and gravel mines upstream in Maryland.

In the District, the river also continues to be contaminated by sewage overflows from the city's 19th century network of interconnected storm sewer and sewage pipes.

Today, one-third of the city's sewage pipes overflow during heavy rains, spewing raw sewage down storm sewer outlets and into the river.

As a result, more than two dozen fish species have disappeared, the river's catfish are contaminated with toxins and its dark, sluggish water is fouled with litter. River and Chesapeake Bay supporters hope to restore the Anacostia's beauty and health.

"What does this have to do with the Chesapeake Bay?" Lewis Linker of the Environmental Protection Agency asked a group of reporters and environmental officials on a recent tour of the river. "Plenty."

The Anacostia program, he said, "is the future of the bay." The river drains into the Potomac, which flows to the Chesapeake, and any effort to clean up the one helps the other, he said.

In the District, two of the bigger projects planned are the marsh restoration, estimated to cost several hundred thousand dollars, and construction of a $14 million swirl concentrator facility that is supposed to eliminate the worst of the raw sewage overflows.

The Metropolitan Washington Council of Governments, which hopes to begin the marsh restoration work yet this summer, first will haul in fill to build up the banks of the marsh, then try different kinds of marsh plantings to see which takes hold, in hopes of duplicating the project elsewhere. Plants can filter out pollutants and provide a place for birds and wildlife to live, in addition to making the place look better than a bare mudflat.

Inside a small building in the shadow of Robert F. Kennedy Stadium are three 57-foot diameter tanks, gigantic blenders called the Northeast Boundary swirl concentrator that are designed to help sanitize the Anacostia. They, too, are something of an experiment. Depending on how well the tanks work, the District may build other facilities to capture and treat raw sewage before it gets dumped into area waterways.

The tanks and associated machinery are the District's largest contribution to the regional compact to clean the river. The swirl concentrator itself is the largest of its type in the continental United States, said Otto James, chief of the District's bureau of sewer services.

It is also partially operational, and if testing goes well, should be fully working by the end of summer, District officials said. The startup date is already more than a year behind schedule and reportedly more than a million dollars over budget. The Environmental Protection Agency recently sued the city seeking fines because of the tardy completion.

The facility is located at the city's largest single source of sewage overflows, the discharging end of a 23-foot-diameter pipe that begins collecting waste near Howard University. In all, the city has 60 points of overflow discharge.

Now, the 23-foot pipe overflows into the river more than a hundred times a year. The hope is that the swirl concentrator will reduce that to no more than a dozen.

The swirl concentrator has the capacity to handle 400 million gallons of sewage a day, cleaning some and sending the rest to the Blue Plains facility for more sophisticated treatment.

The wastewater first will pour into the swirl tanks, which will separate the liquid from the solids by swirling action.

The facility also has chlorination and dechlorination capacity, and is backed up by inflatable rubber dams inside the overflow pipes to regulate sewage flow.