To complete the healing begun by nature and industry after a disastrous oil spill on the Patuxent River two years ago, Washington's Potomac Electric Power Co. would have to build new havens for wildlife in the marshes of Southern Maryland - and in the farm fields of South Dakota.

That is the proposal from four government agencies, who want the company to spend at least $2.7 million on environmental work intended to make up for the deaths of hundreds of ducks migrating to the Midwest and thousands of wading birds, fish, oysters and other creatures.

A spokesman for Pepco said the utility intends to do what the government asks.

"We have spent more than $65 million to restore that area, and now this is the next step," said Pepco spokesman Robert A. Dobkin.

Government biologists say there are few visible signs of the spill, one of the worst in Maryland history. On April 7, 2000, 126,000 gallons of oil leaked into Swanson Creek from a pipe supplying Pepco's Chalk Point power plant.

At its greatest extent, the spill fouled 17 miles of Patuxent River shoreline. Most of the shoreline is now free of oil, although experts say the sediments in some marshes might remain tainted for 15 to 20 years.

Scientists also say there is invisible damage: Creatures that should be nesting, feeding and breeding along the river were killed by oil or failed to bear young.

"You'd be hard-pressed, boating along the river now, to be aware that a spill ever occurred in the area," said Carolyn V. Watson, assistant secretary of Maryland's Department of Natural Resources.

But the spill's effect "does not end with the immediate damage," Watson said. "You have to look at how it affects future generations."

Watson is one of four trustees who helped put together the government's plan, with representatives from the U.S. Fish and Wildlife Service, the National Oceanic and Atmospheric Administration, and the Maryland Department of the Environment.

No one knows the exact toll, but government biologists estimate that 553 ruddy ducks, 122 diamondback terrapins, 376 muskrats and 5,432 pounds of fish died in the spill.

Humans were affected too - about 125,000 trips on pleasure boats were canceled or spoiled by the spill.

The federal Oil Pollution Act requires Pepco to make up for those losses.

Under the government's plan, the utility would have to seed the river with a 4- to 5-acre oyster reef. It would also have to build a 1-acre sandy beach where terrapins can lay their eggs. And it would have to create a 5- to 6-acre marsh in nearby Washington Creek as a haven for a variety of creatures affected by the spill.

The draft plan, which the public can comment on until July 8, requires that a fishing pier, two campsites and a disabled-accessible boat-launching facility be built in parks along the affected stretch of river.

It also calls for buying conservation rights to farmland in the Dakotas, and re-creating some of that region's lost "prairie potholes" - patches of marsh that are important nesting areas for waterfowl.

Sherry Krest of the Fish and Wildlife Service said that would make up for the deaths of ruddy ducks, which do not live in the Chesapeake region year-round. The birds were in the midst of their spring migration to nesting sites in the Midwest when they were ensnared in the oil, she said.

"They just happened to be in the wrong place at the wrong time," Krest said.

Jim Hoff, a biologist at NOAA, said work required by the plan could begin as early as next spring.

He and the other trustees are optimistic about the proposal.

"Our goal is to make the river better, when all is said and done, than it was before the spill, and I really think that will happen," Watson said.