The Hadid Investment Group of Washington has agreed to purchase the site of the much publicized but still unbuilt "Bay of the Americas" project along the Potomac River south of the Woodrow Wilson Bridge in Prince George's County.

The Hadid Group plans to pump an estimated $1 billion into development of the 485-acre project over the next 10 years, according to sources familiar with the project.

Proposals call for building a 1,000-slip marina, a yacht club, hotels, commercial space and luxury townhouses on 200 acres along the Potomac and on pilings over part of the 260-acre Smoot Bay.

The site is bounded by the Potomac on the west and by the Beltway on the north. Developers contend the project would become as important to Prince George's County as the Tysons Corner area is to Fairfax County.

Developer James Burch, originator of the Bay of Americas proposal, would neither confirm nor deny the sale to Hadid. Burch said he has more than one contract but other sources said that Hadid is the "contract purchaser." "If he Burch has a back-up purchaser, that is his right," the sources said.

Burch said he would not comment on reports by others familiar with the project that he had reached an agreement with Hadid. "If other people wish to confirm negotiations, that is okay. I just do not want to prematurely announce anything. I do not want to damage anything."

Hadid has several major projects under way in the McLean/Tysons area and has proposed an office building for the Koons Pontiac site near Tysons Corner.

Burch, who has several partners in the project, said he has "two sound offers" but added that "neither is a full-fledged buyout." Burch reportedly will remain a minority partner in the venture or hold some management position, depending on how a deal is finalized.

The Hadid group reportedly became interested in purchasing the project six to eight weeks ago, after keeping an eye on it for several years.

The project includes acres of dredged waterfront the developer owns. "The asset of owning the bottom of the river gives us the right to build on pilings out over the water," Burch said.

One major problem that has faced the project since its conception has been lack of access and projected transportation problems.

Burch and his partners recently reached a written agreement with Maryland highway officials to help get access to the site from interstate roads from the Federal Highway Administration. Prince George's congressional representatives also have sought federal help in assuring good roads to serve the project.

Developers have asked the Federal Highway Administration for a direct spur from the project onto the Capital Beltway. In general, the Federal Highway Administration has frowned on entrances and exits from federally funded roads when they are designed to serve one particular project.

Prince George's County recently created a special tax district for the Bay of Americas tract. The agreement provides that the same taxes paid on the property as of January 1983 would be continued to be paid to the county throughout the development. As the taxes go up because of changes in zoning and construction, the difference in the 1983 rate and the new rate would be poured back into the project for "infrastructure improvements such as ramps onto the interstate system and other highway improvements," Burch explained.

Last April, Burch predicted groundbreaking on the massive project would take place this fall. No one would say yesterday when Hadid would be ready to break ground or what changes in the plans might be suggested.

When the Bay of Americas project was first proposed in the early 1980s, it generated criticism from Prince George's residents and environmentalists. In July 1983, the development was unanimously approved by the Prince George's County Council.

Last May, a Prince George's County circuit court judge upheld the county council's rezoning of the project, paving the way for a development that could generate an unprecedented influx of dollars into Prince George's County.