IF YOU COULDN'T get to Rome during the restoration of the Sistine Chapel, not to worry. You can get to the Corcoran to watch experts restore the 18th-century Salon Dore' to its original golden glory.

Like a super-slow-motion sunrise, the salon ceiling is revealing its sprightly motifs and a baby-blue sky that had clouded to gray under two centuries of oxidation, grime and darkened varnish. It will be another year or so before work progresses to the carved and gilded pilasters, wall panels, garlands, mirrors and moldings.

The project, led by Corcoran conservator Dare Hartwell, is largely a matter of undoing earlier "restorations" that mask and mar the masterwork that made the salon one of the focal points of pre-revolutionary Paris.

Infirmities of age aside, the gilded room has been moved twice -- to New York in 1904 and to the Corcoran in 1926. The touch-ups and overpaintings of the inevitable dings and scratches are a restorer's nightmare of varying shades, types of paints and fillers and erratic methods of application.

Scientific analysis of paint samples shows the salon's brown parapet originally to have been cream-colored and the walls off-white instead of gray. Matching the colors and textures of the ancien regime is relatively simple, but the restoration is constrained by the modern conservator's ethic: Do nothing that cannot be undone, because later restorers will have still better methods and materials.

Kibitzing the job is a sidewalk superintendent's dream. The visitor is shielded from winter's blast and surrounded by the French paintings and elegant objets of the Corcoran's Clark Wing, named after Sen. William A. Clark, whose Fifth Avenue mansion the salon once adorned.

Progress is measured in square inches, and often several different techniques must be used within the space of a hand's breadth, especially along the panel joinings of the 45-by-25-foot ceiling mural by Hugues Taraval, completed in 1773. When the restorers find themselves growing impatient, they climb down from the scaffolding and take a break; in restoration, haste makes heinous.

Two years of research preceeded the hands-on phase, and the project is open-ended. The public observation window is like the viewscreen of a time machine, so that we see each newly revealed part of the scene as no one has seen it since the Revolution of 1789. The Comte d'Orsay, who commissioned the salon for his mansion, saw the handwriting on the wall and fled the country before heads began to roll.

Seized by the state, the 1712 mansion, known as Clermont, was used for shops, offices and even as a gym. But what goes around comes around, and in 1838 the house was sold to the Comtesse Duchatel, under whom it once more became a fashionable salon. At the turn of the century her grandson sold the salon ceiling and walls to Clark.

The restoration is expected to cost $670,000. The Corcoran should put a donations bucket by the viewport, because it's so satisfying to actually see where one's money goes. The many friends of the troubled institution may also see hopeful symbolism in the project.

RESTORATION OF THE SALON DORE -- Indefinitely at the Corcoran Gallery, 17th Street and New York Avenue NW. 202/638-3211. Open 10 to 4:30 Tuesday through Sunday and 10 to 9 Thursdays. Admission is $3 for adults, $2 seniors and students and free for ages under 18. Metro: Farragut West. Call ahead for wheelchair access.