When you're picking favorites--favorite buildings, paintings, trees, birds, bars--ice-cold logic plays less of a role than, perhaps, it should. My favorite building in all of Washington is the Corcoran Gallery of Art, and the reasons are hugely, although not wholly, sentimental.

The Corcoran, to me, is a palace of echoes, a palimpsest of remembered people and events--hilarious, bizarre, edifying, moving. The straightforward grandeur of the architecture is thus enriched by experience, and this I think is generally true for anyone who favors a particular place: it is the way we get to know and love buildings.

Still, this personal stuff--this admitted bias--aside, the Corcoran building stands solidly on its own as an architectural achievement of high rank. In placing it at the top of my list I am in good company. Frank Lloyd Wright is said to have opined that it is "the best-designed building in Washington."

All sensible commentators on the art of architecture in the capital city have added glowing words of praise. "The clear articulation of each block, the uncompromising elevations, and the magnificent interior atrium galleries show the Beaux-Arts tradition at its best." So wrote the authors of "A Guide to the Architecture of Washington, D.C.," a slim volume not notable for ungrudging admiration.

Until recently the Corcoran staff had not done much to celebrate its impressive physical plant. It has been understandably concerned with more pressing matters, such as saving the priceless collection of American paintings, plugging leaks in the roof and, most recently, installing a climate-control system to protect the art and to make visiting the upper galleries in summertime a bearable experience.

Last week, however, Corcoran archivist Katherine Kovacs quietly put on view a tiny exhibition of letters and photographs that offers fascinating bits and pieces of the early story of the "new " Corcoran, commissioned because the gallery had outgrown its original structure on Pennsylvania Avenue. After its abandonment the orignial building, designed in 1859 by James Renwick, suffered the trials of government occupancy and threatened demolition before being restored a decade ago and renamed the Renwick Gallery in honor of its architect.

The new Corcoran was designed in the early 1890s by Ernest Flagg, a young, little-known New York architect who had just returned from his studies at the Ecole des Beaux Arts in Paris. Excavation at the new site along 17th Street between E Street and New York Avenue NW began in 1893. An opening ceremony on Feb. 22, 1897, attracted about 5,000 people, including President and Mrs. Grover Cleveland.

One of the interesting questions is why did the Corcoran trustees select the untested Flagg over more illustrious architects? Reading between the lines of the correspondence it is possible to conclude, as Kovacs does, that then, as is now, cost was a paramount consideration.

The trustees simply ignored the suggestion that they invite international stars of the day--Charles Garnier of Paris and McKim, Meade and White of New York, among others--to compete for the project, and then chose Flagg over the distinguished local firms whose designs they had solicited. These included Hornblower and Marshall, whose lengthy credits include the Phillips Collection and the National Museum of Natural History, and Paul J. Pelz, who had collaborated on the design of the then-new Library of Congress building.

Kovacs suggests another time-honored reason: Flagg, lean and hungry, traveled repeatedly to Washington to court the trustees while the others seemed simply to have entered their designs and let them sit. Flagg made the Corcoran's concerns his own, and stole the march on his established colleagues to earn his first major commission.

Whatever the reasons, it was an inspired choice, and a good case for close collaboration between client and architect. That "uncompromising" 17th Street elevation, for instance, with its horizontal elements so decisively emphasized in successive layers from rusticated stone base to richly articulated entablature, was not his first idea. Originally, he suggested a robust columned portico to interrupt this sweeping fac,ade; the trustees, to their everlasting credit, recognized a bad idea when they saw one. They sent him back to the drawing board with the unusual and satisfying results we see today.

One of the major tests of a good Washington building is the way it meets the angled corners that occur wherever the orthogonal street grid intersects L'Enfant's pattern of diagonal boulevards. Dr. William Thornton did the trick in fine fashion at the beginning of the 19th century with his Octagon House; I. M. Pei did it more recently with his National Gallery East Building. In between one would be hard-pressed to find a better example than the graceful curve of Flagg's building at 17th and New York, with its wonderful roof and understated system of ornamentation.

A key test that Beaux Arts architects set themselves--and it still is a good test, of any building in any style--was to achieve a clear, harmonious relationship between inside and outside. Flagg's response to the test was at once inspired, original, and tried-and-true. Each segment of the building relates to the spaces inside: the art school along 17th Street is distinguished by a course of high, arched windows, the hemicycle of the auditorium is nestled into the curve of the building's fac,ade at the corner, and the Corcoran's main atrium is a promise kept inside that long horizontal facade along 17th Street.

The atrium, with its rhythmic march of fluted columns on two levels interrupted by the planned pause of the atrium bridge, is indeed the best part the building, its heart. By envisioning the museum as a temple of the arts, Flagg was using the accepted metaphor of his time, but his originality was to put the temple on the inside of the structure--making a space that is at once orderly and exhilarating. Climbing the great staircase is always an event, a ceremonious introduction to the wonderful, evocative clarity of the space.

A thankful bow is due, also, to Charles Adams Platt, the architect who so sensitively added to this fine sequence of spaces when he introduced the splendid rotunda, so perfectly scaled, of the Clark Collection wing in 1925, precisely at midpoint in Flagg's staircase. After all of this, those magnificent skylit upper galleries of Flagg's museum come almost as lagniappe.

When I first visited the Corcoran in the mid-1960s the art in it was my overriding interest. It is thanks in large measure to the artists who have worked in its spaces--above all to Tony Smith, Sam Gilliam, Rockne Krebs, Ed McGowin, Robert Irwin, Gene Davis, Yuri Schwebler and Robert Stackhouse--that the excitement of the architecture penetrated my thick head, and grew into a lasting enthusiasm. Art museums are, as the architects say, my favorite "building type," and to me the Corcoran is the best of them all.

The archival exhibition, hidden in a rear hallway, will remain on view through Sept. 22. In addition, the Corcoran's education department has produced an extraordinary document, "Architecture is Elementary," to serve as a focus for its imaginative program for groups of elementary- and secondary-school students. There cannot be a better place than Flagg's building for such lessons to begin, and to take hold.