The castoff Carter administration did the nation's capital no favor when, hours before its departure last January, it packed the Commission of Fine Arts with its political friends.

The commission is rapidly losing prestige. And since it is only advisory, the fine arts commission's traditional prestige is all that stands between a dignified, beautiful national capital and the lewd commercial schlock that overwhelms most other American cities.

In one hectic day last week, the commission reluctantly approved a tight townhouse development in Mount Pleasant, told a Sunoco gas station to curb its commercialism, gave a benign nod to the design of a new house at the edge of Rock Creek Park as well as the renovation of a Capitol Hill hotel, took a look at the maquette of a General Pershing statue, fretted about the proposed design of new sidewalk lighting along Pennsylvania Avenue, and made news by voting down a proposed $150 million Georgetown waterfront development it had previously approved.

The vote bodes ill for the immediate future of the waterfront, the city's tax base and, worst of all, for the commission's authority.

Just look at the areas outside the commission's jurisdiction -- K Street, Rosslyn, New York Avenue -- to see what that authority means.

Meeting monthly in the small and crowded back parlor of its converted townhouse on Lafayette Square, the seven-member commission, with a staff of six, reviews and approves the design of government buildings, parks, monuments and medals. The Shipstead-Luce Act of 1930 extended this jurisdiction to cover private buildings in close vicinity of public ones. The Georgetown Act of 1950 made the commission the aesthetic nanny for all of Georgetown.

The Commission of Fine Arts was established by Congress in 1910 and initially consisted essentially of the group of architects and artists, headed by Daniel Brunham, who had designed the Chicago Columbian Exposition of 1883 and launched the "City Beautiful" movement.

The group moved on to Washington at the turn of the century, revived the L'Enfant plan, and designed the federal city as we know it today. The Commission of Fine Arts, in effect, was to watch over the execution of the design and protect its integrity.

The "lay member" of the first commission was Charles Moore, the journalist-critic and former Senate aide who steered the Burnham plan through Congress. The other members were architects Thomas Hastings and Cass Gilbert, landscape architect Frederick Law Olmsted, sculptor Daniel French and painter Francis Millet. It was, Omsted jokingly remarked, "the greatest gathering of artists since the 15th century."

At first, this formula was only tradition. In 1936, Congress amended the 1910 Act to prescribe that the seven "qualified judges of the fine arts," all of them appointed by the president, must include "at least one painter, one sculptor, one landscape architect, and one horticulturist or botanist." The amendment also says that no member shall be appointed to succeed himself.

In the past dozen years this legislation seems to have been ignored.

Lyndon Johnson was the last president who cared. White House and, with it, genuine federal concern for the appearance, dignity and livability of the nation's capital went the way of the New Deal and the Great Society. o

President Nixon appointed members whose contributions to his election campaign seem to have exceeded their contributions to the arts. But Nixon also made two laudable appointments: Commission chairman J. Carter Brown, the director of the National Gallery, and Edward D. Stone Jr., a landscape designer and the architect of the Kennedy Center.

Former President Carter appointed Brown and Stone to an apparently illegal third term and added two architects: John B.l Chase of Houston and Walter A Netsch of Chicago.

In addition President Carter appointed a lawyer from Scranton, Pa., with experience on local architectural and art boards, and, the day before he left office, a public relations man from New York City and a lawyer who was a Congressional and White House aide and is now an art colllector and real estate developer.

Could the Carter White House find no painter or sculptor?

Perhaps, in these slipshod times, there is nothing much wrong with all this. But there certainly is nothing much right with it, either.

J. Carter Brown's commission works as hard as any. In its time, some 70 years ago, the big architectural firm of McKin, Meade & White was almost as dominant in Washington (and in the country) as Skidmore, Owings and Merrill is today. No one questions the enthusiasm, ability or integrity of the S.O.M. men who come from different branches of their far-flung firm.

It may also turn oiut that Harold Burson, the New York public relations executive who is now a Fine Arts commissioner, will reveal qualifications for the job not apparent on his biographical handout.

What is wrong, then, is not so much that the commission has been politicized. It is that the politicians have done it so off-handedly that no one on the Hill and in the media has protested, that the fine arts commission seems to have become just another bureaucratic chore and bore.

Ironically, Washington's citizens seem to care more, and more noisily than ever, about this city's livability, architecture, urban design and historic preservation.

But rather than inform and lead this citizen interest, J. Carter Brown's commission seems to have become increasingly uncertain, shy of the limelight, shy of clear decisions.

Washington is building and booming as rarely before in its history. Yet, the Commission of Fine Arts has given us no indication what kind of city it hopes to see come out of the upheaval.

And now the Georgetown waterfront reversal!

At issue was the final approval of a combined, three-acre residential-commercial building complex by the Western Development Corp. at the foot of 30th Street. After three years of controversy the project, as designed by Arthur Cotton Mooire, was scaled down way below the permitted height and bulk and endowed with a small harbor and other amenities.

The commission and other agencies had reviewed the project several times before. All indicated final approval pending minor changes that were made. Now one of the new members of the commission, Walter Netsch, said he did not like the architecture.

What is more, the argument shifted to the battleground chosen by vociferous opponents of the scheme. Would it not be nicer to have no development at all and build a park instead? And isn't the proposed development in the Potomac floodplain, subject to periodic flooding and thus subject to 1977 presidential directive prohibiting floodplain development?

To be sure, the commission has said all along that it would prefer greenery to architecture on this site. A park, "forever open, free and clear," as was said about the Chicago waterfront, is always a beautiful, virtuous thing.

But unlike Chicago, this city is blessed with much clear and green open space. A Georgetown waterfront park would be remote and difficult to get to. Nor would it be safe in the shadow of an elevated freeway and blocked on two sides by Rock Creek Park and Key Bridge.

But that is academic. There will be no park in tghe foreseeable future.

A David Stockman Memorial Park?

The government, local and federal has made it clear there is no money or intention to buy privately-owned land and landscape and maintain it.

This leaves two alternatives: Either the city or the courts disregard the Commission of Fine Arts and the development proceeds without its blessing.

Or the waterfront remains as is -- a disgraceful blight.

In either case, the Commission of Fine Arts is likely to lose.

And greed and bad taste will endanger much of what it has accomplished in its 71 years.