Some years ago J. Carter Brown, chairman of the Commission of Fine Arts, referred to the embattled Rhodes Tavern as "the missing tooth in the smile of 15th Street."

Brown's clever metaphor stays in the mind because it perfectly sums up an attitude that is obviously ruinous to Rhodes Tavern and, by implication, terribly dangerous to the entire downtown district of which the tavern is so small a part.

It is a fixation upon uniform cornice lines that in Washington, the low city, leads all too often to instant mediocrity, unlikable repetition, unhappy dullness. It is a suspicion of relative smallness that, for esthetic, economic and other justifications, condemns whole city blocks to destruction. It is an attitude that, when put in practice, endorses boxlike speculative office buildings that fill those invisible zoning envelopes all over downtown.

To be fair, Brown was making no such generalizations. He was addressing the specific issue of what to do with a building that is much smaller and not nearly so elegant as its august neighbors.

Rhodes Tavern is a classic leftover--a fine, simple, tiny, late-18th-century structure that somehow managed to survive into the late 20th century. This, in addition to its historical importance, is the main significance of the place: Much of the charm, richness, texture, color, variety and liveliness of our cities is due to such leftovers. Learning how to save them, and to effectively integrate them into networks of much larger new buildings is one of the central architectural challenges of our time.

In the fast-rebuilding, old downtown district of Washington, it is the one design issue that overrides all others, because no matter what other good things we do to make the area attractive--plant trees, add benches, place sculptures, open shops, make plazas, form spaces, make places--we cannot regain the scale, history and texture of the old buildings once they are gone.

Rhodes Tavern, of course, is in legal limbo again, awaiting still another court decision that will tell us whether it goes or stays. Should the decision be favorable to the building, it may go, anyway, because the judge must decide only if demolition need be postponed until Washington voters have a chance to express an opinion on the matter in November's election. Should most voters decide they'd like to see the building kept, there's no telling what will happen because their opinion would not be binding--it would be strictly advisory.

One would hope--and it is perhaps a distant hope, after five years of fruitless negotiation--that the developer (the Oliver T. Carr Co.) of Metropolitan Square, the huge new commercial project that threatens to overtake the tavern, would find a way to refinance the development to include the old building, and that the architects (the Washington office of Skidmore, Owings and Merrill) would find a reasonably felicitous way to design around it.

Ironically, Carr is the developer who undertook the laudable task of restoring and adding to the Willard Hotel, and the local SOM office is the firm that came up with an agreeable solution to the same kind of problem (for a different developer) when designing a new office structure now under construction behind the Demonet Building, another leftover landmark structure downtown. (The Demonet is the brick building with that picturesque corner turret at Connecticut Avenue and M Street NW).

The tragic thing is that the Rhodes Tavern decision was made in strict observance of the excellent set of rules established to protect the important relics of our past. Carr does indeed have a perfect legal right to tear this building down (the only legal issue now is whether it is before or after the election). I can fully understand Carr's exasperation--rules are rules and he played by them--though in retrospect it does seem to me that when Carr presented his list of options to the city five years ago he cleverly stacked the deck against the tavern.

I would hate to see Rhodes Tavern torn down--really hate to see it happen. Though legal, and procedurally correct, it would be the wrong thing to do in esthetic, environmental and economic terms. The Metropolitan Square project, while praiseworthy in many respects, is in relation to this excellent, historical building a misguided design based upon a misguided philosophy.

If there is a silver lining to the whole sorry episode it is that the Rhodes, though unique in historical terms, is not by any means the only fine old building left in the old downtown. The dispute over the tavern has tended to obscure these important facts: There are entire clusters of attractive buildings downtown, and there is time left to save them. What has been lacking, so far, is the will.

Despite the triumphant reopening of the Old Post Office two weeks ago, this has been a bad year for preservation in Washington. The city's historic preservation office has been beset with administrative, budgetary and leadership woes. It was, among other things, temporarily suspended from the all-important federal lifeline this spring by the National Park Service. In addition, the Barry administration seems to have been engaged in covert warfare with the Joint Committee on Landmarks, the reviewing agency that limped along gamely until it was replaced, last summer, by the new Historic Preservation Review Board appointed by the mayor.

But it must be remembered that many of the pieces are in place for an excellent, enlightened preservation program in the downtown district (and indeed throughout the city). The 1978 preservation law, though it went wrong in the Rhodes Tavern case, has done much good and is a tool of tremendous potential. The proposed preservation element of the comprehensive plan establishes sophisticated, comprehensive and comprehensible new standards and procedures for preservation and new construction in historic districts. Despite the inexperience of most of its members (glaringly in evidence at its second meeting last week) the new review board, a home rule agency, has a wonderful opportunity to become the efficient, fair-minded, expert body envisioned by the law.

There are, though, two gigantic missing pieces: leadership that can only come from the mayor or his top people, and a downtown historic district. The absence of the latter is clear evidence of the lack of the former, for the downtown historic district, designated by the landmarks committee after months of careful deliberation, has been gathering dust in the District Building for more than a year.

All that is needed to put this district in place is a simple letter to the National Trust for Historic Preservation. For the future appearance and long-term economic appeal of our city, no more important letter could be written. But someone will have to convince the mayor of this. A vote for Rhodes Tavern in November, even if it does not save the building itself, might help.