Developers who are proposing a $500-million waterfront complex at the Prince George's County end of Woodrow Wilson Bridge across from Alexandria say it will be the biggest project fully visible from Washington's 66-mile Beltway -- "more visible than even Tysons Corner."

The Smoot Bay development, which will have its first hearing next month, is one of the most ambitious proposed for Prince George's County, sponsors of the proposed "Bay of the Americas" said last week.

But the very size of the development and road access problems may invite federal and local opposition and could force the developers to scale down the project, some observers believe.

Plans call for a 1,000-slip marina and yacht club, waterfront restaurants, a conference center and town houses built on pilings over the tree-lined bay, as well as one or two 12- to 14-story hotels, eight- to 10-story office buildings and a total of nearly 1,000 residential units.

The developers maintain they have "overwhelming support from almost everyone" for rezoning the land for the project, including most of the county's civic and business groups as well as county officials.

But some residents of the Oxon Hill-Fort Washington area say they are concerned about increased traffic the complex would generate and at least two federal agencies are concerned about a dense high-rise development on the Potomac River shore.

The National Park Service owns the northern third of Smoot Bay as well as a crucial strip of land needed by the developers for a major roadway to connect the two parcels of land the developers have options to buy.

Park Service Regional Director Manus (Jack) Fish last year wrote the Prince George's County Council expressing "concern" about the proposed development and urged the county to consider buying the vacant land and turning it into a public marina and park. The county already has two parks there, including Oxon Hill Manor, the 1920s mansion of Sumner Welles, adviser to President Franklin D. Roosevelt.

The National Capital Planning Commission, federal planning agency for the Washington area, wrote a similar letter and will consider the project at its October meetings.

In a move to support the development and permit the access road, the Prince George's Planning Board has asked the U.S. Department of Interior to transfer the Park Service lands around Smoot Cove to the county for neighborhood park use. The developers anticipate that the county would allow them access across the land.

Interior has taken no position on the transfer request. It would require an act of Congress to transfer federal land to the county, however, and the county might be required to pay fair market value for it.

Developer John Burch claims the Park Service has no need or plans for the land and already controls almost all the Washington-area waterfront. "The government owns 96 percent of the 44 miles of waterfront around Washington . . . and most of it's underused. . . . There should be room for people who don't ride bikes or throw Frisbees."

County officials already have endorsed development of the Smoot Bay area. New master plans call for making it a regional waterfront center that will "be a fitting gateway to Prince George's County and the State of Maryland."

Burch said his "Bay of the Americas" complex is designed to do just that: it would give Prince George's a prestigious waterfront that "will make Old Town (Alexandria) and Georgetown drool with envy."

However, the master plan states clearly that any development for the Smoot Bay site is contingent upon a new access road that will prevent additional traffic congestion on already overcrowded Oxon Hill Road.

Burch, a Fairfax County developer and former speech writer for Sen. Joseph Biden (D-Del.), and his partner, Oxon Hill developer Frank Lucente, have optimistically said they "have solved the access problems" for their development.

Burch insists that if Interior won't tansfer the land to the county or allow a road across it, much of the Bay of Americas can be built without it on the two separate parcels. However, the high-rise waterfront hotel probably would be dropped and the southern parcel would be mostly residential, he acknowledged.

About half of the 442-acre site is under water up to 30 feet deep. It was zoned for half-acre rural residential lots before the old Smoot Sand and Gravel Co. dredged the area, thereby flooding it. Burch says the zoning would permit him to build nearly 300 houses with the present zoning. The change to the mixed-use zoning he is requesting would permit about 980 housing units, including 41 luxury waterfront villa estates and town houses built in several rows on pilings in the bay. The piling construction is possible because "we own the underwater land," said Burch. The U.S. Army Corps of Engineers will have to approve the piling construction but Burch is optimistic about getting corps approval.

State Del. Charles Blumenthal (D-Oxon Hill), who lives nearby, praises Burch for scaling down "the monster plans" he first proposed.

"He came in here like a bull in a china shop . . . proposing a huge development to be built in two years. . . . But he went out like a lamb who doesn't want to overwhelm the area," Blumenthal said. "He's now proposing a phased development over 10 years, with the major part after the state builds the I-295 extension in 1987. I can't say I'm opposed or in favor until I see the current plans."

A $25 million to $30 million extension of I-295, now designed to parallel the Beltway and merge into an enlarged Indian Head Highway-Beltway interchange, would help relieve traffic jams that plague the present intersection and would ease any increased traffic from the Bay of Americas project.

Yet early completion of the I-295 project depends on the availability of federal interstate highway funds to help finance it, and federal officials contend the planned road is ineligible for such funding. If "the state has to fund it, it might not be built until much later," Hal Kassoff, state highway director of planning, said last week.

The major entrance to the Bay of Americas would be on Oxon Hill Road near the Beltway interchange with Indian Head Highway. A second major entrance would be needed further down Oxon Hill Road if the developers cannot gain access across the Park Service land.

Burch's application to have the two parcels rezoned will be heard Oct. 27 before a county hearing examiner in Upper Marlboro. It is on the agenda of the federal NCPC for its Oct. 7 and 21 meetings. The project also is expected to be given a public hearing before the county planning board later this fall.