If one doesn't look twice at the leasing agent's sign on the fence surrounding the great hole at K and 20th streets NW, it seems just another abstract graphic. But a second look shows a cropped vision of a gun-metal gray turret thrusting through a blue sky, the kind of peak architects stopped putting on building tops nearly 100 years ago.

The sign doesn't lie. The office building under construction there will indeed rise to a pinnacle -- three pinnacles, in fact -- and if this stylistic exercise doesn't seem so unusual at a time of revived revivalism, the location for it is wildly improbable.

The site is flanked by two of the worst offenders on a street full of offensive buildings. Directly across 20th Street, on the southeast corner of the intersection, is the extraordinarily monotonous Esplanade, a structure I think of as the Chocolate Mud Factory because of the off-putting milkshake hue of its metal cladding. To the west there is 2020 K, another blandly brutal office building, the sole redeeming quality of which is that the bilious brown color of its metal spandrels doesn't call too much attention to itself.

Architect David Childs of the Washington office of Skidmore, Owings and Merrill clearly is having a bit of fun at the expense of his bad neighbors by turning the strategy of contextual architecture upside down: Instead of blending the new with the old he inserts a piece of the "old" into the new. "The context I was thinking of is Washington the way it used to be," he says.

This seems fair. After all, K Street west of 17th has been so horribly treated in the last two decades by a sequence of coarse, hand-me-down Modernist office buildings one might argue that the best way to fit in would be to design an ugly building. But there are places where a building should outshine its neighbors by setting a good example, and this is one.

Besides, despite the stylistic incongruity, the new structure fits in rather well. In many respects this is the basic K Street speculative office box as determined by the zoning regulations: eight stories high, with a minimal (though handsomely appointed) lobby, two underground parking levels and the standard Washington structural system of concrete columns arranged in 20-foot bays. The difference is that this box is quite beautiful.

The client deserves some of the credit. "We gave only two directions," says Ron Goode of the Farragut Development Co. "We wanted a first-class stone exterior and some kind of contoured roof." Still, the architects deserve the lion's share for taking this ball and, quite amazingly, taking off with it.

Childs took his cues from time-honored Washington architectural motifs -- the turrets, the striped masonry, the impressive cylindrical curve of the main corner -- and from the beauty and civility of Parisian streetscapes. The result is a large, powerful structure that is, at the same time, inviting.

It is arguable that Washington buildings, because they are so close to the ground, need even more visual interest at the top than skyscrapers, but until recently it's an argument most of this city's postwar architects have ignored. The turrets of this new building, at once forceful and romantic, will be the most emphatic reminders in many decades that the city deserves, and needs, a variegated skyline.

And they will be, by Washington standards, very high, rising 130 feet from ground to pinnacle, and, counting the flagpole atop the central, cylindrical turret, to 160 feet. That is as high as any structure in the city can go (and at that, only along the north side of Pennsylvania Avenue between the White House and the Capitol).

There's nothing illegal in this -- so long as they are not inhabitable, any and all "spires, towers, domes, minarets, pinnacles" and other decorative elements may rise above the permissible roofline, in accordance with the Height Limitation Act of 1910 -- but we must credit Childs and his colleagues for reading the law and taking full advantage of it.

In addition, as they did at the top of the impressive building at 1300 New York Ave., these architects also integrated the "service penthouse envelope," so often just a nasty-looking appendage, to help bring the design to a nifty conclusion at the top. The tiny, window-like medallions in the masonry striping along the upper edge of the building, for instance, hide window-cleaning equipment, but their primary purpose is ornamental.

Nor did architectural ingenuity and skill cease at the top. The new building, in the traditional way, has a distinguishable middle and bottom, as well. The ground-level street frontages are appropriately attractive, with bright canvas awnings above shop windows and a base where rows of limestone blocks alternate with courses of soft reddish granite. The striping is simpler in the middle floors, but monotony is avoided by dint of careful detailing of the window openings.

In fact, the treatment of the windows is exemplary throughout, as if the designers were again giving lessons in how to achieve a lot with a little. There are at least six different window shapes in the fac,ades, and each has been carefully detailed. The flush rectangular windows of the middle floors, for example, are nicely articulated, first with a sharp reveal and then with projecting sills, while shop windows at ground level are set back two feet from the building line.

It is, all together, just a wonderful piece of work that makes one anxious for the fall of 1986, when it will stand there putting its neighbors to shame. There are those, I suppose, who would still insist on calling such designs outlandish and retrogressive, but I can only see this one as something fresh and new -- a sign not only of what this fast-rebuilding city once was, but also of what it can again be.