They started digging the hole at 1718 Connecticut Ave. NW last Wednesday. Normally this is no cause for celebration -- a parking lot disappears in favor of yet another humdrum office building in the sawed-off Washington style.

This time, however, there is reason to shout hooray. The office building that David Schwarz of Architectural Services (Richard Bornemann, project manager) designed for this low-lying stretch of boulevard is in nearly all respects an exemplary sign of the times.

Schwarz's building will be anything but sawed-off. It celebrates the skyline with a vigor unique among recent Washington buildings. Its stylistic eclecticism is as obvious as it is noteworthy--1718 Connecticut is the first really strong Post-Modernist building to go up in Washington.

What are the sources? The architect says that his scheme of putting the heaviest of the building masses at the corners was inspired by H. H. Richardson's muscular design for Trinity Church in Boston. But the most impressive elements of the building--that huge, set-back clock tower on the south, its truncated reflection on the north, the gabled mansard roof, the forceful entrance bays and the powerful contrasts of brick and limestone surfaces--constitute a full-throated tribute to the hearty Victorian buildings of Frank Furness of Philadelphia.

Unlike most office buildings, whatever their claims to stylistic distinction, 1718 Connecticut is fully designed on all four sides. Schwarz and his colleagues paid careful attention to the shape and placement of the windows and surfaces on the sides of the structure, and thereby partially redeemed its one major fault: its size.

Despite all of their appropriate, history-quoting ingenuity, the architects could not entirely disguise the fact that the building towers over its neighbors. They did do the next best thing, though. They made it interesting to look at.

And then, with a sense of play characteristic of a younger generation of architects (Schwarz is 30, and his office colleagues are about the same age), Schwarz tacked a giant surprise onto the back of the building. In contrast to the 19th-century flavor of the brick and stone facade, the alley side of the building will have a sleek, stucco-covered skin with no-nonsense square windows and a string of rounded columns: shades of Corbusier right out of Richard Meier's New York book.

Hinted at in the angled change from brick to stucco on the northern and southern sides of the building, this clever about-face converts 1718 Connecticut into a self-contained lesson in architectural history. With an emphatic flair it makes the point that here is a genuinely contemporary building and not merely a worshipful repetition of the past.

If Schwarz's design is an inimitable tour de force, it nonetheless points up the fact that, even in relatively modest or mediocre new buildings, we are beginning to see a respect for the existing urban context that was anathema to orthodox Modernism, not to mention unheard of among most of the city's developers.

A few blocks south along Connecticut Avenue, for instance, at its intersection with Hillyer Place, the GMR firm of Gaithersburg (Ralph Hurst, architect in charge) has attempted to pay respects to the early-20th-century vernacular in a nearly finished seven-story office building that, as of old, has a beginning, middle and end: articulated stone entranceways at ground level, neat window bays complete with keystones, and a cornice line with honed-down moldings.

Despite some nice touches, what this building inspires the most is wistfulness. To take a look at any of a dozen or so buildings downtown -- the delicate Sheraton Carlton Hotel at 16th and K streets, for example, or the wedding-cake confection of ornament on the Southern Building at 805 15th St. NW -- is to lament that the skill is gone.

Gone, that is, except in the hands of a gifted maverick like Schwarz. Of course, behind every good building, almost always, there is a good client, an owner with the wit and will (and money) to insist upon, or at least to appreciate, superior design. In the case of 1718 Connecticut there are two such clients.

Schwarz designed the building two years ago for a public-spirited, preservation-minded team of Washington lawyers who, in addition to making money, wanted to do something to halt the parade of chunky mediocrities creeping north along the avenue from downtown. "Actually, as developers we were just a bunch of amateurs," one of the group explained. "We got into the thing by accident when we bought the buildings next door (1722 and 1724 Connecticut) with the idea of restoring them. The owner wouldn't sell without the parking lot, so we ended up with an empty lot and, eventually, decided to try to put up a building that was economically feasible and decent to look at."

The project languished because of fluctuating interest rates until this summer, when the group decided to get on with it. Enter client No. 2, Mike Windsor, a local real-estate executive who just last June opened a Washington office for Lincoln Property Co., a big southwest development firm. "I had my eye on the 1718 project," he said, and he made the lawyers an offer they couldn't refuse. The company bought the project whole on Tuesday and the digging began the next day.

It was a fast move and an unusual one, Windsor admits, but "we wanted to start our Washington operation with a project we can be proud of." (At about $67 per square foot, compared to $50 or so for an ordinary speculative office building, costs are high, but Windsor seems optimistic that the ingenuity of the design will attract rents to match.)

What everybody involved got for their money and good sense is an innovative, trend-setting structure, a creative solution to the vexing problem of how to make a forceful architectural statement and yet remain reasonably compatible with a row of pleasant, smaller, older neighbors.