An exciting new architecture is suddenly emerging in Washington.

It fills out rows of Victorian townhouses which, as much as the monuments on the Mall, contribute to this city's unique charm.

Most of the Brobdingnagian buildings of the past 50 years have tried to ruin this charm. A few are obtrusively ugly, like the FBI Building, or gaudily vulgar, like some of the private office buildings around K Street.Others try for distinction with some affection or another, self-conscious about being in the capital.

The currently most fashionable affectation is sticking obese concrete columns all over the facade, which makes large office or apartment buildings look as though they were constructed of sewer pipes.

Another current vogue is building set-backs in the shape of dog legs, giving us oddly angled widenings of the sidewalk. I suppose we should all be grateful to gain a little more public open space. But that is Manhattan's problem, not ours. L'Enfant gave us, if anything, too spacious a city plan. And since Washington's builders rarely provide amenities -- such as fountains or benches -- on this extra pavement, all it does is catch litter.

We have jubilant specimens of modern architecture, such as I. M. Pei's East Building of the National Gallery and Philip Johnson's little Pre-Columbian art museum at Dumbarton Oaks. But few, if any, of them are commercial or residential buildings.

In the category of what architect Paul Rudolph has called "background architecture," the 19th century did better than the 20th century. But neither did modern architecture do as much harm to our city as it did to others. The height limitation has kept Washington from getting too high on modern.

Indications are that the current building boom is also bringing us an esthetic boomlet -- architectural design which is little better than that of past few decades. Builders and architects, it seems, no longer feel that they have to show off their modernity -- or even their buildings. They curry favor, instead, by attempting to blend in with their newly popular historic neighbors and by giving us conveniences, such as arcades or mid-block passages. n

Such is the state and reputation of modern architecture today, that the developer and architect who happen to find an old building on their site consider themselves lucky.

The new Pennsylvania Avenue, for instance, promises to be architecturally distinguished, not because of any dazzling modern design, but because the new buildings modestly defer, by and large, to the architectural tone set a century ago.

The most dominant building along the west end of Pennsylvania Avenue will not be the giant blockbuster between the National Theater and 14th Street, but the renovated Willard Hotel and its addition -- a whimsical echo of little Willards, designed by architects Hardy, Holzman, Pfeiffer.

The next most intriguing building design so far approved for the avenue seems to me to be the electric concoction of old and new buildings designed by Hartman-Cox and to be known as 1001 Pennsylvania Avenue. The complex incorporates the old U.S. Storage Building, one of most handsome commercial structures downtown, to be remodelled by architect David M. Schwarz.

Even more encouraging than these big jobs is the unaccustomed quality of a large number of small custom jobs all over town. Small but beautiful row houses are filling in vacant lots all over the center city.

According to a recent finding of the House Subcommittee on the City, headed by Henry S. Reuss (D-Wis.), about a quarter of the average American city consists of unused land, either held out of the market by real estate speculators waiting for a killing, or simply abandoned.

A few years ago, it was deemed economically unfeasible to fill these gaps. The lots were too small for profit.

That has now changed. The much cited, affluent "young professionals" want to live in the city. Small law firms and professional organizations of all kinds are willing to pay more not to be housed in slick, modern office buildings. "Redlining," the refusal of the banks to make construction loans in the inner city, has been made illegal.

Suddenly, there is an insatiable market for downtown "infill" buildings.

Far too many of them are produced like fast food -- a hasty concotion of high-tech ingredients made to appear as something it is not, but appealing to the popular taste. The fact that these "antiqued" brick boxes have to be squeezed into narrow lots and kept to low heights makes them fairly inconspicuous, if not palatable.

But a considerable number of intriguing and stylistically innovative infill houses, designed by young architects working for young clients or developers, has popped up in the cityscape or on the drawing boards in the past few months. There must be at least a thousand in downtown Washington.

"There is a sort of 'underground,' a 'young old boys' club,'" says David Schwarz, Yale '74, who has a thriving infill practice. "Its members are architects, lawyers in the big law firms like Arnold & Porter or Williams and Connolly or sons or nephews of successful developers. None of us is over 35 years of age. We all still carry much of the idealism of the '60s around with us. We love downtown Washington. We want to do something for the city. But we don't have the clout or money to do super-blocks. In fact, we hate super-blocks. So we do infill houses."

Robert G. Kicherer, 38, a developer who is currently building four infill building, says the vast number of details and bureaucratic obstacles that must be overcome takes all the enthusiasm young idealists can muster. "Yes, there is good money. But there are also enormous risks. It is like gambling. Before you know it, you are over your head."

With architect Reid A. Dunn, Kicherer is building a small office building at 1708 Connecticut Ave., that consists of two townhouses, connected by a simple glass structure. This infill echoes the bays of the old houses and continues their horizontal lines. Its drawing looks stunningly modern and yet pleasing and fitting. The glass emphasizes the strong and architectural character of the old building in a way no rigid replica could.

"We will not be able to get away from glass," says Schwarz. "It is just so much cheaper and simpler to work with than other building materials."

Schwarz is using a lot of glass -- in fact he has designed a box of that most hateful of all building materials, reflective glass -- for the corner of 17th and Q streets, to be used as a condominium residence. At the apex of that corner, taking up about a quarter of the facade, he put a Victorian-style, rather ornate masonry design, turret and all.The masonry does not stop in any defined way; it sort of dissolves into the building's glass curtain. The glass reflects more (and more genuine) Victorian houses across the street.

It is esthetically daring, on the border of picturesque mannerism. But I think I am going to like this building.

At first glance, another Schwarz infill building, at 1718 Connecticut Ave., looks as though it were built in 1890. Only when you look more closely, do you discover that only the shapes are Victorian. The details are honestly of our time. Yet, there is none of the definantly naked Bauhaus "honesty" in Schwarz. He does not think "ornament is crime." He loves ornament, buys it out of catalogues and sticks it gleefully whereever he thinks appropriate.

Similar infill architecture is practiced by several other young architects about town, including another young Schwartz, Robert, who has designed a most interesting mini-row of three townhouses for Woodley Place NW. The proposal called for two units in each house. The lower units were to have front yards, the upper units were to have prominent roof terraces. The character of their architecture was determined by some old trees, which Schwartz designed around, and some old masonry walls, which David Schwarz incorporated in his design. The project changed hands, though, and the new developer is not ready for something new and different.

Arthur Cotton Moore has designed an unusual facade (backed by a humdrum interior) for the Georgetown Mews, an apartment and duplex apartment house on 29th Street, opposite the Four Seasons Hotel. The brick facade, with its rich variations of rounded and angular bays, decoratively (rather than functionally) placed windows and all manner of sculptural treatment, is pure Expressionism, such as was found in European architecture between Art Nouveau and Art Deco. It is almost gaudy in brick and skillfully done. I find it more pleasing that startling.

The whimsy, the still slightly wicked use of ornament and the uninhibited ingenuity of this new electicism, smacks of the self-conscious Post-Modernism that is so fashionably exhibited in New York. David Schwarz vehemently denied that he is a Post-Modernist. I think he is right.

Post Modernism, as they tout it in New York, is a polemic rather than architecture. It makes use of historic forms and ornaments, but only to enlarge them way out of proportion or apply them in some other hairy way, designed to shock rather than please. They show the frustration of function rather than follow it.

What Schwarz and the other Washington architects are doing is architectural design in historic context. They use old ornaments because that helps them to harmonize their new buildings with their old neighbors. Besides, these old ornaments are pleasing, much as old pictures on the wall or old silver on the table.

In short, the new election is not, or not yet, an architectural Weltanschauung.

It is a way to fill in the gaps we have left or bulldozed in our historic districts.