When Richard Nixon ordered wrecking crews to tear down the old Navy buildings on the Mall along Constitution Avenue in 1970, he made it perfectly clear what he wished to see on that choice Washington ground.

There, amid the museums and monuments, the president wanted an American-style version of one of his favorite parks, Tivoli Gardens, the famous carnival of amusements, rides and restaurants in Copenhagen. Said Nixon: "Something like Walt Disney would do."

But in matters of esthetics and architectural tastes, Nixon would learn, there is a force in the nation's capital more powerful than the White House. It is The Commission of Fine Arts, a little-known band of seven presidential appointees who, with a modest budget and no legal powers, exercise extraordinary influence on the appearance and shape of this city.

The commission favored a sylvan setting to replace the Navy buildings on the Mall, and that's what it eventually got there with the construction of Constitution Gardens -- a pond, an island, some trees and walkways.

The episode over the would-be Tivoli Gardens illustrates a basic fact of life in Washington that architects and developers are still learning: The Commission of Fine Arts may lack specific legal power to veto the whims of presidents and those of lesser standing, but, more often than not, it still gets it way.

Made up of seven unpaid appointees from throughout the nation -- mostly architects and people with some training in the visual arts -- the Fine Arts Commission for 70 years has played a greater role than any other government entity in shaping the way Pierre L'Enfant's original design for Washington is carried out.

"You always have developers who are in the free enterprise system who are looking for intensity of use," says Edward D. Stone Jr., a member of the commission for 10 years."We have to look at the city in a different way."

In short, Washington, many say, would be a vastly different city if there were no Fine Arts Commission.

Charles H. Atherton, the commission's pipesmoking secretary and unofficial historian, recalls that among other projects, the commision over the years has stopped the military from building the Pentagon at the end of Memorial Bridge, just across the Potomac River, and a Veterans Administration from building a hospital overlooking Arlington Cemetery.

"That would be great [for hospital patients] to look out and see all the graves," Atherton commented.

"We're the visual conscience for the capital," says J. Carter Brown, commission chairman and director of the National Gallery of Art here.

The Fine Arts commissioners wield enormous power, using their own subjective eye to decide what is good design, what is appropriate for the specific environment of different neighborhoods and what complements existing structures.

What is the secret of the commission's power?

Put simply, Brown says, it is the tradition and the prestige of the commission. The District government, he notes, for example, has rarely rejected the advice of the commission.

But behind that are two other potent factors: private developers realize that the city government is loath to grant them building permits for projects the Fine Arts Commission disapproves, and the commission can "delay" review of projects it does not like -- delays that translate into money lost for anxious developers.

Also, says Brown, "the city is probably wise enough to realize" that esthetic improvements in Washington can be economically beneficial in attracting tourists from throughout the world.

Still, lacking the outright legal sanction to veto proposals brought before it, the Fine Arts Commission often has to hope that the personal and professional stature of its members and the fact that the commissioners are appointed by the president will carry enough clout to kill projects that it thinks are esthetic abominations.

James O. Gibson, the District government's planning director who must deal with the intermeshing of city and federal interests, says the local government occasionally disagrees with Fine Arts' recommendations, but "the city generally feels it is well guided" by commission advice.

The Fine Arts Commission is, Gibson said, "an organic part of the city's review process. There's not inherently a conflict between the federal and local interests. The city's interest in enchancing the ambience is very real."

The process of obtainng a city building permit varies widely from one development to another, and may require the approval or review of several agencies, including the Fine Arts Commission. If a developer needs a zoning change on a piece of property, for example, he must win approval for it from the D.C. Zoning Commission.

He may then have to seek review by the Fine Arts Commission, depending on the type and location of the development. In addition, the developer may have to submit the proposal to the Joint Committee on Landmarks if the project is in a historic district of the city or involves demolition of a historic building.

Finally, representatives in Mayor Marion Barry's office review construction projects before the city decides to issue a building permit.

David Childs, the architect of the Constitution Gardens project on the Mall and one who has made many development proposals to Fine Arts, said the commissioners have "a lot of popular support because they usually have the right answers" on questions of taste and design.

However, Childs said, the commission's "real threat is delay," the power to postpone approval for construction projects until the proposed design is to its liking.

"Time is money," concedes Brown. "We try not to hold them up unless it's necessary for the project" or to preserve the public interest.

The commission's geographical and esthetic jurisdiction is at once broad and specific. Among other things, it is charged with reviewing proposals for all new federal buildings, statues, fountains and monuments in the District of Columbia; all city government structures; all new federal and city parks in Washington; any private building that borders the Capitol, the White House, downtown portions of Pennsylvania Avenue, the Mall, the National Zoo and Rock Creek and Potomac parks; and any construction in the Old Georgetown area.

Also it reviews plans for American battle monuments throughout the United States and overseas, advises on the designs for U.S. medals and coins and responds to general questions of art about which the federal government is concerned.

The commission has no official jurisdiction in Virginia and Maryland, except for advising on the selection of parkland in the National Capital Region of the National Park Service.

Various federal agencies, however, have often asked for commission advice on projects in Virginia and Maryland such as renovation work at Dulles International Airport and the monument to President Lyndon B. Johnson, along the George Washington Parkway.

As often as not, the commission's role has been to reject what it considers to be bad design or construction that would change the character of the city that is supposed to be dominated by the Capitol and other monuments.

Stone, a Fort Lauderdale, Fla., landscape architect and son of the Kennedy Center's architect, says, "Unfortunately, a lot of our work is not encouraging outstanding design, but discouraging horrors."

Fine Arts' impact has been significant in other ways, such as when the first commission more than half a century ago recommended placement of the Lincoln Memorial on its present site, despite the fact that Congress objected that the location was both remote and malarial.

Or just recently, when the commission rejected a proposal for a massive condominium-commercial complex on the Georgetown waterfront because it looked like a "beached whale." That effectively forced a developer to forfeit his $150,000 investment in the plan and hire a new architect to redesign the project. Even so, the commission's preference still is to have the waterfront turned into a park.

Sometimes the commission's impact is trivial, such as the other day when it reviewed a gold medal the U.S. Mint is designing to recognize Kenneth Taylor, the Canadian ambassador who helped spirit six American diplomats out of Iran.

At its typical monthly meeting, the commission usually considers a dozen or more proposals -- a lighting scheme for the Smithsonian Institution's castle building, sculptures for Walt Whitman Park, a major condominium complex overlooking Rock Creek Park, fences for the Brazilian Embassy, a private residential swimming pool in Georgetown, a couple of office buildings, awnings for the Hay-Adams Hotel. All, along with the Taylor medal, were on the commission's June agenda.

While the commission's mandate is broad in some respects, it can also be limited. The commission, for example, had no authority over the designs -- some of them sharply attacked by architecture critics -- of the new office and commercial complexes built in the last decade along K Street NW and other nearby downtown streets.

The commission also has had no authority, much to its continuing dismay, over the galloping development of high-rise office buildings in Rosslyn, across the Potomac River in Virginia.

The Fine Arts Commission intervened in a court case brought by the Interior Department seeking to limit the height of the builings constructed in Rosslyn. But a federal judge and an appeals court ruled that the federal government had no right to limit their height.

The decision left several of the Fine Arts commissioners chagrined and with a sinking feeling that their own efforts to enhance the design of Washington would be partly thwarted by intense development across the river and in close proximity to the federal monument area and Georgetown.

Brown, gazing over a spectacular view of the Capitol from his National Gallery office, speaks pointedly of the Rosslyn case. "Rosslyn is a visual belch in the landscape. Luckily, there's not too much land" for more development.

Rosslyn, says Victorine Du Pont Homsey, a retired Wilmington, Del., architect and another commissioner, is "awful, horrible, outrageous in every way."

Predictably, Arlington planners vigorously reject such assessments. Thomas Parker, the county's deputy planning director, says he thinks the two buildings in dispute in the lawsuit "are handsome structures. Both buildings add a great deal to Rosslyn, both to the skyline and within Rosslyn itself."

Parker contends that the overall skyline of "Rosslyn is far enough off the axis of the monumental core that it doesn't intrude on one's view from the monuments" on the Mall.

Fine Arts member Eli S. Jacobs, a New York investment banker, says the commission failed in controlling the height of Rosslyn buildings, two of which will reach 31 stories, "because we didn't have the jurisdictional authority. We will have in Rosslyn the appearance of a commercial city that we do not now have."

The result, he said, will be to undermine the height limitations in Washington that the commission has guarded over the years as jealously as a child protecting a lollipop. In fact, the commission was once dubbed "the skyline commission" and Atherton views "the maintenance of the skyline" up to now as one of the panel's "most important" achievements.

"It's always a struggle to preserve the wonderful scale of Washington," said Frederick D. Nichols, a University of Virginia professor of architecture and another commissioner. "All the pressures are for bigger. Every developer wants to use every inch he can."

Some developers, however, have become at least temporary converts to the commission view.

Herbert S. Miller, the Georgetown waterfront developer, went away frustrated after his first design was rejected. But he admitted that his second proposal "turned out to be a better project. I have found Fine Arts to be demanding, which it has a right and responsibility to be."

Other developers have stormed away frustrated and not come back. In the late 1960s, before the current commissioners took office, Washington realty entrepeneur Mallory Walker tried to win approval for an office building in Southwest Washington. But after making repeated proposals and switching architects, he gave up.

Brown, the 45-year-old commission chairman, waxes poetic about the designs he likes, but discusses with equal enthusiasm those he doesn't. Witness the Tivoli Gardens tale.

Nixon aides, Brown recalls, "made the Interior Department throw in every imaginable gewgaw. It was chock-a-block full.

"The commission was appalled," said Brown, his voice still exuding disdain for the decade-old proposal.

The commission decided that while a Tivoli Gardens-type amusement park might be appropriate somewhere in Washington, the place certainly was not the Mall. It wanted to preserve the Mall as a sweeping expanse with the national symbols of the Capitol and monumental tributes to two of the country's most famous presidents, Washington and Lincoln.

By making a variety of suggestions of what might be more suited to the Mall, the commissioners eventually whittled Nixon's Mall proposal to its present state, the idyllic Constitution Gardens.

Similarly, the immensely popular Air and Space Museum once was proposed to look "a little like an aircraft carrier that got stuck here when the flood receded," Brown said. However, he added that he is pleased with the result -- a smaller, glass and marble structure.

But Atherton also notes that the city government has rejected some Fine Arts recommendations. On occasion, for example, it has ignored entreaties that various Georgetown buildings be preserved and instead has permitted their demolition.

Then there's the story of the FBI headquarters building, which Brown describes as "one of the blots" on the commission's history.

Fine Arts eventually approved the design of the FBI building, which several commissioners now regret. Atherton says the fortress-like building is "hostile, it's very formidable. I don't enjoy being near it."

The commissioners wanted to have sidewalk cafes, bookstalls and other commercial ventures on the street level of the building, to make it "more human," they said.

But as everyone in Washington found out sooner or later, the FBI's late director, J. Edgar Hoover, always got his way. There would be no stores in the FBI building, Hoover said. The building that now bears his name sould be built the way he wanted, Hoover decreed, not the way a group of esthetes at the Fine Arts Commission wanted. And Hoover, of course, got his building.