In a surprise move, the federal Fine Arts Commission yesterday reversed itself and rejected plans for a controversial $154-million residential and commercial development on the Potomac River shoreline in Georgetown.

The action of the commission, which only last spring gave preliminary approval to virtually the same plans, could mean the tawdry waterfront with its cement plant, trashh heaps and parking lots may remain unchanged for as long as another decade.

Both District of Columbia and National Park Service officials said they have neither plans nor the estimated $40 million to $70 million needed to buy the six acres of privately owned land on the waterfront and no plans to develop a park on the 13 acres of publicly owned land, all located between the Whitehurst Freeway and the river.

The District currently is reviewing building permit applications for the complex of 350 luxury town houses, shops and office proposed for the waterfront by the Western Development Corp. However, city officials said yesterday permits are unlikely to be issued in the wake of Fine Arts opposition to the project.

The 70-year-old commission reviews the proposed designs of numerous federal and private development projects in Washington and its opinions are advisory. But Washington officials have rarely rejected them.

Yesterday's decision brought applause from a crowd of more than 75 people -- many of them Georgetown residents who have lobbied for years for creation of a waterfront park -- who jammed into the small town house offices of the commission on Lafayette Square. But it came as a surprise to officials of Western Development, who have been trying to win approval for its development plans on the six acres for almost three years.

Western's architect, Arthur Cotton Moore, told reporters after the 5-to-2 commission vote, "I think we got caught in a commission change. All but two members are new and had never seen the plans before. We've been before the commission and its Georgetown Board six times and they agreed withus and supported the plans. Everybody liked it," Moore said.

The outgoing Carter administration appointed five new members to the seven-member commission, three last November after the election and two several days before leaving office.

Moore told the commission after the vote that he expects the Georgetown waterfront development issue "will end just where everyone always expected it would, in court."

Houston architect John S. Chase voted to reject the waterfront plans, saying, "I think we need to take into consideration the citizens not just of Washington but the entire country. I don't see how we can do anything but reject it."

Commission chairman J. Carter Brown, director of the National Gallery of Art, said one concern was that the entire development would be within the Potomac River flood plain.The waterfront has been inundated during three floods since 1936. Carter's 1977 presidential order directs federal agencies not to approve development within a flood plain unless there is no practicable alternative Brown said the Justice Department recently informed the Fine Arts Commission that commission decisions are affected by that order.

Brown also said the commission's long-standing position favoring park land along the waterfront should be retained, despite the commission's earlier preliminary approvals of Moore's design centering on a curving structure surrounding a pool. He added that he was concerned that if the commission approved this project it could set a precedent for other development along the waterfront.

Brown and Edwad D. Stone, a landscape architect and the only othher holdover commissioner, voted against the project, as did three new members -- Chase, Chicago architect Walter A. Netsch and Harold Burson, head of a New York public relations firm. Voting for the project were Sondra Myers, a "lay" member from Pennsylvania, and Alan Novak, an art collector.

Donald F. Shannon, president of the Georgetown Citizens Association, told the commission that the Western project "has no regard whatsoever for the Georgetown Historic District . . . by luck we'vre never had any development [except the cement plant] on the waterfront. I hope you will say there shouldn't be any."

Opponents of the development included nearby Advisory Neighborhood Commissions and a coalition of more than 25 civic and environmental groups. Shannon presented a letter from D.C. Mayor Marion Barry favoring a park along the waterfront, although he did not actually oppose the Western Development project. The District has offered its waterfront land to the National Park Service, because Barry has said the city has no money to develop or maintain a waterfront park. The Park Service also says it has no money and new Interior Secretary James Watt recently announced a moratorium on the purchase of federal park land.

The only waterfront park land proposed has been by Western Development officials, who said they would contribute half of Western's six acres for public open space, spend $500,000 to develop open space, spend $150,000 to develop a park between 31st Street and the foot of Wisconsin Avenue, spend $1.28 million "for aesthetic improvements" to the Whitehurst and Potomac freeways and spend $1.75 million to develop public areas within the project, including a pedestrian bridge over Rock Creek along the Virginia Avenue right-of-way. CAPTION: Picture, A plan of the controversial $154 million residential and commercial development on the shoreline in Georgetown. The Washington Post