District government officials have cleared the way for a $154 million residential and commercial project and a floating restaurant along the Georgetown waterfront.

Carol B. Thompson, Mayor Marion Barry's agent for historic preservation, yesterday reaffirmed a decision she announced last month to permit construction of a six-acre complex of shops, offices and luxury condominiums on the watefront site, located between the Whitehurst Freeway and the Potomac.

Meanwhile, the District's Department of General Services has agreed to a 20-year lease of adjoining city-owned waterfront to the owners of the former presidential yacht Williamsburg. The owners, who will use the site for parking, plan to convert the 50-year-old vessel into a posh restaurant and dock it there.

Both plans had been opposed vehemently by Georgetown citizens' groups who had argued that the properties, which stretch from the Potomac River north to K Street NW and from Rock Creek Park west to 31st Street NW, should be used as a waterfront park.

The restaurant agreement was signed on Oct. 15 by Carroll B. Harvey, then city director of general services, who resigned the next day to enter private practice as an engineer. It calls for the yacht's owners, who include Stuart J. Long, a restaurateur and major Barry fund-raiser, to pay the city $37,500 a year. The city also will receive 2 percent of the restaurant's gross revenues when receipts exceed $500,000.

Don Shannon, president of the Citizens Association of Georgetown and an outspoken opponent of waterfront development, said the twin decisions would result in "an unplanned disaster."

"These people city officials must have holes in their heads to do this," he said. "The Department of General Services is bananas."

Another community activist, Katharine Sullivan, described the restaurant lease as a reward by Barry's administration for the political contributions of Long and his partners.

"Clearly, these are people who are very close to the mayor, so he is going over everyone's the citizens' association objections and giving his friends what they want," she said.

Herbert S. Miller, president of the Western Development Co., which controls the six acres involved in Thompson's ruling, praised the decision, saying: "We're obviously delighted that we finally have the chance to clean up the waterfront with a handsome development."

Thompson's newest decision, which is almost identical to one she issued on Sept. 12, held that the planned development, with its elliptically shaped buildings, conforms in height, texture, color, style, building materials, arrangement and appearance with the Georgetown historic district.

She was forced to rescind her Sept. 12 decision the day before it was to go into effect, after lawyers for the citizens' association and other groups opposing the project charged that she had made an improper visit to the waterfront before issuing that ruling.

The Citizens Association of Georgetown, long the most vocal opponent of the projects, contends that the proposed buildings are too big, tall and bulky, and are completely out of character with the Victorian and Federal-style homes that dominate Georgetown.

Leaders of the association, who indicate that they probably will appeal the decision to the D.C. Court of Appeals within 15 days, said the parking lease contradicts the commitments made by Mayor Barry to save the 12 acres of city-owned property for parkland.

But Donald L. Croll, chief of the real estate division of General Services, said the land is only a small sliver near Key Bridge, and should not effect longstanding city plans to turn over what city-owned property remains to the federal government for a national park. U.S. Interior Secretary James A. Watt has said, however, that the Reagan administraton opposes any expansion of the park system.