At the northeast corner of the intersection of Connecticut and Rhode Island avenues stands the Longfellow Building, considered Washington's first truly "modern" office building. To emphasize its importance as an interrupter of the city's classical tradition, the American Institute of Architects' Washington architectural guide quotes Alice from Lewis Carroll's "Through the Looking Glass": "It's very rude of him, she said, To come and spoil the fun!"

This fun-spoiling building, with cantilevered balconies stretching across its Connecticut Avenue facade and its service core contained in a separate vertical shaft, indeed marked the beginning of architectural modernism's dominance over downtown Washington real estate.

The Longfellow Building was designed by William Lescaze in 1940, nine years after he and architect George Howe designed what is considered the first international-style skyscraper in America, the Pennsylvania Savings Fund Society tower in Philadelphia.

Swiss-born Lescaze was one of several European architects who ushered in modernism from across the Atlantic. Before World War II, political pressure had forced the closing of the Bauhaus school, and many of its faculty -- Walter Gropius, Mies Van der Rohe and Marcel Breuer, among others -- came to the United States.

The American architectural avant garde, taste-makers and academics viewed these men as apostles bearing design theories that would leave behind revivalism and historicism. Long before they departed Germany, the internationalists were sanctified by Henry-Russell Hitchcock and a youthful Phillip Johnson in their 1932 Museum of Modern Art book "The International Style," which influenced many young architects.

Gropius and Breuer went to Harvard to teach, while Mies went to Chicago and the Illinois Institute of Technology. Beaux Arts methods, values and faculty were purged. Bauhaus pedagogy and international-style design quickly spread, destined to dominate American architectural education, and American architecture, for the next 25 years. And downtown Washington, despite its classicist past, would not resist modernism's arrival; classicist "fun" was suspended.

Along the streets and avenues of the monument and commercial areas, one sees countless office buildings that represent architectural modernism's effect on the capital's postwar, central-city growth. Although facades vary, there is, nevertheless, a certain sameness because of consistent heights and repetitive collonaded bases.

Behind these facades are the flat slabs, column grids, duct work and service cores -- elevators, fire stairs, toilets, utility rooms and vertical shafts -- that are practically interchangeable from one building to another. They provide the flexible, efficient space that Louis Sullivan, Gropius and Mies said was needed for human use in the 20th century. They also express the cost-effectiveness and marketability demanded by real estate developers.

Therefore, facade manipulation -- particularly where so many privately owned buildings were constructed on in-fill lots (as opposed to being free standing) -- became the only way to achieve expressive differentiation. But was expressive differentiation desirable? Earlier manifestos had suggested otherwise. Modern architects had limited tactical choices when manipulating facades if they were to remain faithful to their credos of "less is more" and "form follows function."

A modern building's exterior was expected to reveal in some rational way little more than its skeletal organization, its floor lines and its dimensional modularity and standardization. Moreover, it was wrapped with a "curtain wall" of relatively minimal thickness hung on the structural frame.

Lots of large, fixed-glass windows were mandatory for light and view; energy was cheap and abundant then. Vertical mullions between each window marked the intersection of the partition layout grid -- typically based on 4-, 5- or 6-foot modules -- with the exterior surface, the point where interior partitions could abut the window wall.

In turn, some kind of facade element had to occupy the space between the sills of windows on one floor and the heads of windows on the floor below. Thus, the facades of office buildings seemed well suited to the horizontal, continuous-ribbon-window strategy that arose in the 1920s and '30s. Alternating bands of transparent glass and opaque spandrels -- these could be of brick, precast concrete, stone, metal or opaque glass -- became a favored mode of expression.

This could be further modified and, presumably, enhanced by adding vertical elements to the curtain wall. Thin mullions between windows could be enlarged and stretched vertically up the facade, overlaying both the window and spandrel planes.

Or the architect could telegraph the presence of structural columns behind the curtain wall by widening or thickening only those mullions aligned with the column grid. Such mullions then looked like columns. They, too, could be extended vertically up the entire facade, much like a raised pilaster on a classical facade but without the ornamentation.

Still another facade strategy entailed fabricating the curtain wall in large standardized panels, either of metal or precast concrete, spanning from floor to floor. These panels could be one or more window modules in width.

As methodical and limiting as these strategies may sound, substantial variety and decorative effect nevertheless could be achieved. Architects varied the size and proportion of windows, window mullions, window frame details and curtain wall joint details. Materials could vary greatly in texture, from smooth and slick to rough and reliefed. Modernist dogma dictated that buildings should be monochromatic, but accent colors on integral components were acceptable.

Designers could manipulate the character of the ground floor and the way buildings met the sidewalk by pushing back the plane of storefronts while increasing ground floor height. This left the structural columns in place to form an arcade adjacent to the sidewalk. Window displays, signage, planting, accent lighting and some entrance "statement" were intended to complete the picture.

Before being transformed and implanted in Washington, much-publicized modern office building prototypes had been done elsewhere by well-known architects for well-known clients. Among the most famous are New York's Lever House, designed in 1950 by Gordon Bunshaft of Skidmore, Owings & Merrill, and the Seagram Building, by Mies and Johnson, completed in 1958. Both are on Park Avenue.

Perhaps more than any others, these two buildings and their architects influenced commercial and corporate architecture throughout the world for almost two decades. Literally hundreds of facsimiles and adaptations exist. In D.C., it is easy to find office buildings that look like sawed-off or stunted versions of these or other similar projects.

The zoning height limit often made Washington's versions of these structures appear to be the bottom third or fourth of an itinerant New York skyscraper. Along H, K and L streets between 15th and 21st streets, you can see plenty of mutations. Slightly taller ones may be seen in Rosslyn and scattered around the metropolitan area.

Interestingly, the architectural debates of the 1950s and '60s weren't between classical and modern stylists. Instead, they were between architects who, while unquestionably modern, rejected the purist, utopian precepts of orthodox internationalism in favor of their own personal, stylistic mannerisms. They believed modernism was not a style. There were alternatives to the steel, concrete, brick and glass boxes so vigorously embraced by architects and their clientele.

NEXT WEEK: Modernism diversifies