The federal Commission of Fine Arts unanimously recommended yesterday against construction of an elaborate condominium and commercial development on the Georgetown waterfront despite a developer's offer to scale down the project to meet architectural objections.

Saying the proposed development "looks like a beached whale," commission chairman J. Carter Brown, director of the National Gallery of Art, and five other commission members said the now tawdry Georgetown waterfront should instead be bought by the federal government at an estimated cost of up to $40 million and turned into a park.

The commission's action does not kill the proposal for the 350 $200,000 to $300,000 waterfront condominiums, but at the very least casts a cloud over an agreement sanctioning the project signed last July by the D.C. and federal governments and Western Development Corp.

The commission's recommendation now goes to D.C. Mayor Marion Barry, who has the final decision on whether to issue the building permit for the development. Barry's chief planning aide, James O. Gibson, signed the July agreement and voiced support for the project at yesterday's fine arts commission meeting.

However, the commission's recommendations are rarely rejected.

Under the estimated $60 million proposal, a joint venture of Chessie Resources and Western Development would build the residential and commercial complex on 5.9 acres betwen the Whitehurst Freeway and the Potomac River, west of Rock Creek, while the National Park Service would build a riverfront, 160-foot-wide strip park on 12 acres in front of and adjoining the development.

The park and development proposal, if actually constructed, would replace what Brown called "one of the great eyesores of America," the existing waterfront combination of massive concrete-making machinery, a public parking lot, a lumberyard and a lot where the District impounds towed cars.

Despite the current jumble on the Georgetown weaterfront, Brown said the commission feels that "any building here is a mistake."

The commission along with numerous Georgetown residents, instead support purchase of the tract, which extends to just west of Key Bridge, for a park sloping upward from the river to hide what everyone agrees is an ugly highway, the elevated Whitehurst Freeway.

Sen. Mark O. Hatfield (R-Ore.) and Rep. Fortney H. (Pete) Stark (D-calif.) have introduced legislation to buy the land for a park, but no hearings have been scheduled on their bills.

Brown said that the prosposed development would produce "so much of the same thing," a three-to-six-story, terraced brick structure that would stretch for 1,180 feet along the waterfront.

Grosvenor Chapman, a former president of the Georgetown Citizens Association, complained that the development would block the river vista from Washington Circle and hide part of Key Bridge.

Chapman showed the commission a slide picture of the bridge from Washington Circle, but conceded to a Western Development official that he had taken the picture with a telephoto lens.

Western Development's president, Herbert S. Miller, told the commission that his firm would change several proposed features about the development that the Board of Architectural Consultants for Georgetown had found objectionable, including elimination of the fifth floor of the project and bridges containing residential units across 30th, 31st and Thomas Jefferson streets.

After Brown and the other commissioners criticized the development plan, a frustrated Miller asked whether the commission wanted more dense development on the tract, which is legally permissible under current zoning.

"What we'd like to see is none of the above," Brown replied, "and that's very difficult to legislate.'

Miller said after the meeting that his firm would consider whatever suggestions the commission might make about the development. But he said that if the current proposal is rejected, Western Development would consider using the existing zoning to build a more massive complex.