THE LIBRARY OF CONGRESS is divided into three parts -- the Jefferson Building, the Adams Building and the Madison Building, each very unlike the others. In 1897, the Thomas Jefferson Building opened -- a paean to Italian Renaissance architecture, setting the standard for "library architecture." Hired to decorate it were 52 artists who outdid themselves: The whole of the building's art and architecture is greater than the sum of its parts. And the building oozes with symbolism.

Entering its Great Hall is like walking into a vast, three- dimensional illuminated manuscript: Murals, mosaics, marble and gold cover every corner. Climbing the bannisters of the staircases here are what "The Guide to the Library of Congress" calls "cascades of marble babies"; each represents an occupation.

In the upstairs corridors of the Hall, real children run, yelling echoes to each other under the vaulted, painted ceilings. Above them, painted women represent Lyric Poetry, the Graces and so forth; particularly lovely are the "Five Senses" painted by American Impressionist Robert Reid.

It really is endless. Take special note of Elihu Vedder's marvelous mosaic, "Minerva," at the end of the Hall near the Visitor's Gallery. Roman goddess of wisdom, she's the Library's patroness -- symbolically, of course.

The other breathtaking feature of the Jefferson Building, the Main Reading Room, measures 150 feet from floor to dome. Above the three kinds of marble here (Siena, Tennessee and Algerian), eight plaster statues stand for aspects of civilization; each with two bronze statues beneath it, such as Homer and Shakespeare for Poetry, and Moses and Saint Paul for Religion. Of special interest, Herodotus was done by Daniel Chester French, who sculpted the Lincoln Memorial Lincoln.

The dome -- the crowning touch of the vast chamber -- was designed by Edwin Howland Blashfield to laud and magnify the glorious name of learning. Twelve winged figures, each 10 feet high sitting down, surround a circular painting called "Human Understanding." The 12 figures in this collar-like mural represent the Middle Ages and the 11 countries or civilizations that Blashfield thought had the greatest influence on America.

Behind the Jefferson Building, in the John Adams Building, opened in 1938, one finds the occasional Art Deco touch. But this is hardly a tourist attraction. In the building's most aesthetically interesting room, the Social Science Reading Room on the top floor, readers appear deep in serious study. One feels vaguely uncomfortable staring up at the two panels by Ezra Winter that depict the pilgrims of the Canterbury Tales -- the murals are faint, faded masses of horse legs -- wondering which pilgrim is which. But the view of the sunset from the west hall of the fifth floor is superior, with the dome and lantern of the Jefferson Building resting on the horizon, where evening stars mingle with airplane lights.

Across the street, the James Madison Building, opened in 1980, is often called ugly. Mainly an office building, it has its selling points, however. The Atrium on the first floor is an undiscovered oasis of quiet where a napping bureaucrat may be stretched out in shirtsleeves on a stone-bench pallet near a fountain. On the sixth floor, the cafeteria -- selling inexpensive fare of inconsistent quality -- commands a grand and dramatic view of steeples, smokestacks, freeways, Capitol Hill townhouses and a river or two.