He probably spent more time in the halls of Congress than anyone alive. His tenure spanned eight presidents. He delivered no speeches, authored no bills, made no political enemies. Yet, when he retired last week, Allyn Cox left a legacy more durable than that of almost any congressional mover-and-shaker one could name.

Cox, 85, is a muralist, a latter-day Michelangelo commissioned to emblazon four great vaulted corridor ceilings on the House side of the Capitol with the pageant of American history--to glorify the seat of modern democracy as his 16th century predecessor did the Renaissance Vatican.

Inch by inch, stroke by stroke, Cox has daubed his way along hundreds of feet of ceiling since 1951, creating what Capitol Historical Society president Fred Schwengel calls "the greatest addition to the art of historical painting in the world today."

Cox, a sprightly, squinty man in rumpled work clothes spattered with paint older than some sitting congressmen, is clearly uncomfortable with such high praise. Still, of the inevitable comparison with Michelangelo, he says puckishly: "Well, the ceiling of this corridor is longer than the one in the Sistine Chapel."

Except for the convenience of electric light, things have not changed much over four centuries for the ceiling painters of the world. Cox spent most of his workdays perched atop a giant scaffold, putting final touches on the second of the four ceilings. Surrounding him, six feet below his massive plaster canvas, was the clutter of his art -- brushes and tubes of paint scattered on a table at his side; drop cloths, oily rags, half empty cans and cartons at his feet; study sketches propped against packing cases or taped to the wall.

How does a bespectacled, 85-year-old man paint a mural on a ceiling? "Slowly" said Cox in an interview just before his retirement. Still, he was in constant motion as he painted, leaning close to add a line and stretching back again to gain perspective. He steadied his stroke with a stick propped under his painting hand and sighted along his brush at the ceiling, rather like a sharpshooter aiming at a target.

"I started on this end with a painting of the women's suffrage parade in New York in 1918," he said, pointing to a group of stern-looking women in stern-looking dresses. "I know two women who were in that parade who are still alive. I finished down at the other end with the signing of the Mayflower Compact in 1620. William Brewster, one of the authors, is an ancestor of mine."

Each of the five-by-six foot panels that form the 172-foot long mural is a product of patient, painstaking research and planning. He spent years doing rough sketches, drawing full-color studies to scale, ordering the scenes for continuity, and sketching life-size paper mock-ups. Those he perforated and traced onto the ceiling surface before the actual painting began. "I also drew the major figures in a scene--Ben Franklin, James Madison--in the nude first," he explained, "to get the proper drape of their clothes later on."

The heroic figures (now fully clothed) who peer down from Cox's ceilings comprise an illuminated biography of America: Here is Lincoln delivering his second inaugural address; John Paul Jones raising the first American flag; Theodore Roosevelt surrounded by a crowd of anxious journalists; Washington and Hamilton working on Washington's farewell address to his officers; Patrick Henry in full fiery oration. The Lincoln panel is based on a photograph, Cox explained, "and historians have actually identified John Wilkes Booth as one of the people standing in the crowd."

Interspersed among these epic heroes and events, Cox has portrayed a series of more humble, though equally important, aspects of the American experience: a British official collecting taxes from a colonist; the withdrawal of Union troops from the South; factory girls working in a New England mill; a black man voting for the first time. So much less boring, Cox said, "than a bunch of old men signing papers."

Against all probability, Cox's first commission at the Capitol fulfilled a longing he had nurtured for nearly half a century. "When I was very young," he said, "my parents brought me here and showed me an empty space in the frieze under the Rotunda dome. After that, I used to dream and dream of painting it one day." The dream came true during the Truman administration, when Cox was selected to fill the 32-foot gap in the frieze with paintings depicting the Civil and Spanish-American wars and the birth of aviation. "It was the greatest day of my life," he said.

Cox's parents helped him launch his career in more practical ways. His father--himself a painter--taught him how to paint "when I was barely strong enough to hold a ruler for him to draw a line." After mastering "the things not studied anymore, like perspective and anatomy," Cox said, he was awarded a fellowship at the American Academy in Rome, where he studied mural painting. He returned to the United States after World War I and his mother became the aspiring muralist's first customer.

"It was in New York back in the '20s . . and I convinced my mother to let me cover a room in her apartment with a mural. When I finished, we had a party and invited some people--architects, decorators, you know--to see my work." The idea, Cox said, was new at the time. "I didn't just paint a wall. I painted everything. The entire room was a mural." The response, according to Cox, was overwhelming, and eventually earned him commissions to paint murals in the homes of such patrons as railroad tycoon W.K. Vanderbilt and Vincent Astor, well-known socialite and director of the Western Union Telegraph Company.

When the Great Depression settled in, Cox recalled, "people stopped building grand, expensive houses, so I moved over to public buildings. Things were pretty grim for a while, but I managed to eke out an existence." He did it by painting murals at the University of Virginia's law building in Charlottesville and the W.A. Clark Memorial Library at U.C.L.A.

"Then came the big break," Cox said, referring to the Captol Rotunda commission, "which happens only once in an artist's lifetime." Following close on its heels were commissions at the George Washington Masonic Memorial in Alexandria and at Dumbarton Oaks. Cox also painted a small mural with a more modern twist on the Senate side of the Capitol--an oval moonscape of the first lunar landing.

It now is left to his assistant, 62-year-old Cliff Young ("The most perfect assistant anyone ever had," Cox said) to complete the second ceiling and move on to the third, the theme of which is to be "Westward Expansion." For that one, Cox had planned a composition of primitive maps plotting the progress of pioneers across the continent, highlighted by paintings of Indians and frontiersmen.

That plan will be followed, despite Cox's retirement. The student would not consider rejecting the work of the mentor. "Musicians don't change the notes when they play Beethoven," explained Young. "It's the same thing."