The three buildings on Wisconsin Avenue make an unlikely trio. Occupied by Fannie Mae, the giant home mortgage company, they differ almost dramatically from each other. But by their very differences they encompass much of Washington's postwar architectural history. Each in its way is typical of its time.

Our story begins and ends with the little building, recently remodeled, at 3939 Wisconsin Ave. NW. Designed by the firm of Aubinoe, Edwards and Beery for a group called the National Radio Institute and built in 1956, it lacked the populist design flair of much '50s commercial work, but wore frugality like a badge. Timidly progressive, with a flat roof and triple rows of picture windows, it was mindful of tradition too, with bricks laid in Flemish bond above an inset, fieldstone-sheathed ground floor.

A year later, directly across the avenue at 3900 Wisconsin, arose another office building, much more prepossessing despite being set way back from the street -- it was like the big house in a cleared colonial field. Designed by the Washington firm of Chatelain, Gauger and Nolan for a large insurance company, it was modeled on the 18th-century Governor's Palace in Williamsburg. The edifice became more impressive still when symmetrical wings -- Williamsburg-like in detail but larger in scale -- were added north and south in the early '60s.

This building too was typical, the kind of architecture on which Leon Chatelain Jr. had built a successful Washington career. "Chatelain was not our ideal or idol from a design point of view," a younger, hipper competitor once recalled, "but he got a lot of work from banks and institutions because he performed very responsible work."

The happenstance face-off of the modest modern building with the earnest revivalist one illustrates a fact often ignored in architectural history books, even books about Washington. For good or ill, depending on the writer's bias, the decades immediately following World War II usually are characterized as a period of triumphant modernism. But this is true only up to a point.

Though modernists were indeed doing much of the biggest and most of the best architecture of the time, buildings in traditional American styles, designed straightforwardly and without postmodernist irony, maintained a steady popularity in and around Washington and other Eastern Seaboard cities. The battle of the styles began to attract serious critical attention in the '60s (the 1966 publication of Robert Venturi's "Complexity and Contradiction in Architecture" signaled the change), but it had been fought year in and year out along streets such as Wisconsin Avenue.

Skipping to the late '70s, when Fannie Mae (the Federal National Mortgage Association) purchased the Chatelain building, our story acquires a contextualist theme, which has been so strong a part of Washington's architecture for more than two decades. The new owner decided to add another wing, this time to the back of the building, and selected California architect John Carl Warnecke to do the job.

Warnecke's 1979 addition, hidden from the street, is handsome and adroit -- it abjures the colonial detailing but matches the materials, layout and scale of the original building, and encloses two shady, commodious formal courtyards. This pleasant, humane result is hardly surprising -- Warnecke's mid-'60s work around Lafayette Square, saving the 19th-century texture of the place while adding two new government buildings, contributed significantly to the contextualist movement here and nationwide.

Next came the boom of the middle '80s, and with it the big building at 4000 Wisconsin, adjacent to the Fannie Mae headquarters. Announcing the arrival of self-conscious postmodern architecture on the block, the building accommodated another Fannie Mae expansion.

It aroused justified neighborhood antagonism because of its size and the bulldozer mentality with which it was rammed through. Of special concern was the way it gobbled up space at the rear of the site, encroaching on the narrow northern end of Glover Archbold Park. Designed by the Washington firm of Stinson Capelli, the building is by no means a uniform aesthetic delight. Proportions are awkward all around, and the top floor is particularly graceless -- it should have been shorn off or, at least, stepped back.

Even so, there are redeeming qualities. Housing a multiplex movie house and street-front stores, this is a genuinely mixed-use building in a good urban site. The central courtyard is an amenity for Fannie Mae workers and neighborhood residents. The pyramidal glass corner towers look a bit tacky, as if adorning a birthday cake for I.M. Pei, Mr. Pyramid himself, but they're kinda likable -- the building definitely is the better for having them. Likewise, the patterning of the brick and precast concrete facades, a jumpy update of the staid Williamsburg materials and rhythms next door, leaves a friendly impression.

Which brings us back to the modest little building at 3939 Wisconsin -- it never offended anybody, but, after years of wear and tear, it didn't please anybody either. Fannie Mae bought it a couple of years ago to create a separate office for its Housing Impact Center. This itself is a worthy endeavor -- the focal point of Fannie Mae's programs for low- and moderate-income housing, the center clearly deserves an identifiable home of its own.

The Washington firm of AI/Boggs was hired to do the remodeling. There's a smidgen of irony in the choice. Joseph Boggs, the firm's talented design principal, is a committed modern architect whose best building to date, the Machinists Union Headquarters in Prince George's County, is a song of glass, steel, concrete and stone. But on Wisconsin Avenue we can literally read his mind as he makes the moves of a practiced Washington contextualist.

First, he manifestly understood that the client wanted to make a family out of its three disparate buildings. Second, he realized that to do this he couldn't turn his back on 4000 Wisconsin, although, he says, "it's not one of my favorite buildings." (One can't imagine Chatelain's building as a Boggs favorite, either.) Third, step by step, Boggs and colleagues took a bit from here, a bit from there and, through revision and refinement, put the pieces together.

The result is an odd combination of the pat, the pleasing and the poetic. The pat part has mainly to do with the windows -- converted from '50s rectangles of glass to false double-hung sash, they're funny-looking approximations of the proper Williamsburg proportions across the street. It might have been better not to have tried. Also predictable, though not unsatisfying, was the decision to give the building a conventional base, middle and top. This works because it corrects a curious defect of the original design -- the inset ground floor -- and because of the refinement of the details.

One still tends to pass the building without taking much notice, mainly, I suppose, because one tends to pass it in a car. But if one does pause, there are things to look at and take pleasure in -- the horizontal ribbing in the new concrete base, the taut steel lintels and entrance canopy, the well-proportioned pyramidal tower at the building's canted northwest corner.

More than any other single thing does this corner pyramid, a refined version of the towers atop 4000 Wisconsin, give the building a new presence on the street. Still a modest building, 3939 is now modestly poetic.