The eventual shape of the Georgetown waterfront became clear yesterday: Part of it will be a park, but it will be flanked on one side by a massive condominium, office and hotel complex, and on the other by a floating restaurant in the USS Williamsburg, a one-time presidential yacht.

The waterfront's future design was unveiled by Mayor Marion Barry on a Potomac River cruise that featured a wine-and-cheese buffet lunch, a duo playing quiet jazz and a score of D.C. government officials who were aboard to extol the shoreline development projects being carried out under the administration.

Last year, a group of Georgetown citizen activists and environmentalists lost their battle to have the entire 19-acre Potomac River shoreline from Rock Creek to Key Bridge turned into a park when construction started on the ritzy Washington Harbour condominiums and adjoining office buildings.

Yesterday, they lost two more decisions.

The National Park Service announced it is lifting a 20-foot height restriction on the narrow strip of land between 30th Street NW and Rock Creek and giving a Dallas-based hotel chain the right to build a 91-room, 52-foot-high luxury hotel and a 60-foot-high office building next to the Washington Harbour project.

In exchange, the Washington Harbour developers granted the park service permanent public access along the riverfront and Rock Creek and said they will donate $1 million toward development of the waterfront park.

Meanwhile, Barry said he will ask the City Council to approve the transfer of nine city-owned acres along the waterfront between the Whitehurst Freeway and the Potomac to the park service for use as a park.

But Barry also said that, contrary to the wishes of the activists, part of the land will be used for a parking lot for the restaurant in the Williamsburg, the yacht used extensively by President Truman and briefly by President Eisenhower.

"I believe in balanced development," Barry said during the three-hour Potomac cruise, which was paid for by Western Development Corp., the developers of the Washington Harbour project.

"I don't believe the city can have all of anything," he said, alluding to the citizens' efforts to turn all of the once-industrial waterfront into a park. "I have to be concerned about what's best for the entire city. I know there are some of you who don't agree. That's what democracy is all about."

Manus J. (Jack) Fish, the park service's regional director here, approved the lifting of the height restriction less than two hours before the cruise. He did so by accepting an appraisal by his financial experts that showed that Western Development's swap of the waterfront access rights was worth $102,144 more than the lifting of the restriction. Federal law requires that the swap be equal or favor the government.

Cornish F. Hitchcock, a lawyer for various citizen and environmental groups, said the park service's appraisal will be independently reviewed. "If our appraisers tell us it's not an even transaction, there's always the possibility of going back to the park service to try to reverse the decision or going to court," he said.

Robert D. Zimmer, president of Rosewood Hotels Inc., which will build and operate the hotel, said construction on the $58 million hotel-office complex will start in March and be completed in early 1987.

Juan Cameron, president of the Citizens Association of Georgetown, said his group is "going to fight very hard" against Barry's plan for use of the Williamsburg as a waterfront restaurant.

"We're outraged," Cameron said. "It's very crass to have a national park created after 20 years of discussions and then have some private corporation use part of it as a parking lot."

The Williamsburg is now owned by restaurateurs Richard J. McCooey and Stuart J. Long, a close political ally of Barry's and a member of the D.C. Armory Board. But McCooey said yesterday they were unable to obtain the $3.5 million to $4 million needed to restore it.

As a result, McCooey said, the boat, now docked near the Blue Plains sewage treatment plant, is being sold to Stuart Davidson and John Laytham, the owners of Clyde's restaurant in Georgetown, who plan to refurbish it and open the restaurant.