Sistine Chapel

More than 450 years after he painted the ceiling of the Sistine Chapel, a ''new'' Michelangelo is emerging. The restorers who have undertaken the delicate project of cleaning the ceiling are astounded by what they are uncovering.

''There is a beauty, subtlety, and skill that reveal a Michelangelo totally different from what we expected to find,'' says Carlo Pietrangeli, the Vatican Museum's director.

Even while the Vatican displays some of its other precious treasures in the United States for the first time, it is keeping the doors wide open to its greatest masterpiece throughout the restoration project, which has been under way since 1981 and will take 12 years.

Already, five lunettes over the windows are finished; another three will be completed and unveiled by April. In August, work will begin from a specially built mechanical scaffold on the Story of Creation ceiling.

From under 4 1/2 centuries of soot and candle smoke have emerged bright, light colors no one would have dreamed of by the hand of an artist never considered much of a colorist. A total absence of preliminary cartoons on the walls indicates a speed and sureness rarely, if ever, matched in the quick-drying medium. Michelangelo had a technical expertise in the art of fresco painting few believed possible in an artist, considered even by himself, first and foremost, a sculptor.

With the new discoveries, the restorers are debunking centuries-old Michelangelesque myths.

''When we started to work, we saw that so many things that had been written or said about Michelangelo didn't correspond with what we were finding under the dirt,'' says Gianluigi Colalucci, who is in charge of the restoration.

For instance, it has frequently been said that Michelangelo was a bad fresco painter. Giorgio Vasari, an art historian who was a contemporary of Michelangelo's, wrote that the artist, then 33 years old, had never painted a fresco in his life before tackling the gargantuan Sistine ceiling. In fact, it was the very reason Michelangelo's rivals Raphael and Bramante urged Julius II to award him the commission, believing he would make a poor showing compared to Raphael, and thus fall from Julius II's favor.

Instead, says Mr. Colalucci, Michelangelo was a master of the art. That was fortunate, he adds, for had the great Renaissance painter been less technically proficient, his colors and perhaps his paintings would have been lost forever beneath the thick layers of glue applied by 18th- and 19th-century restorers in a technique used at that time to clean frescoes.

Unlike the thick colors and minute details of other 16th-century frescoes, Michelangelo painted with fluid colors that, now cleaned, seem almost like watercolors. These light colors painted in flowing, impressionistic brushstrokes allowed the frescoes to withstand centuries of water damage. Thick layers of paint trap the dirt and chemicals formed when the wall becomes damp. But restorers have discovered that the thin coats allow the dirt to escape from the wall.

The cleansing process is painfully slow. It took Michelangelo five years with his head thrown back most of the time to paint the ceiling and another two for the Last Judgment scene on the wall. It will take the restorers, working four hours a day and in much more comfortable conditions, almost twice that long.

Where Michelangelo painted an entire 12-foot sybil or prophet in a day, spurred on as he was by a frantically impatient Julius II who wanted to inaugurate the chapel Nov. 1, 1512, the restorers will spend up to two weeks. Only three restorers are doing the work, ''to better control the uniformity of the job,'' explains Mr. Colalucci.

The extreme caution is necessary not only because the frescoes are among the world's greatest masterpieces, but also because Michelangelo was totally unpredictable and resourceful. The restorers have noticed Michelangelo never repeated himself figuratively. Although he followed the fresco technique, the restorers note that he exhibited great freedom in his work.

''So it is difficult to know exactly what lies under these thick layers of glue,'' Mr. Colalucci says.

Fortunately the restorers of Michelangelo's most important work do not share his penchant for the enigmatic. The historian Vasari wrote that the man himself was as secretive as he was brilliant. When he painted the Sistine Chapel ceiling , he bolted the doors tight for five years, allowing no one to view the work in progress.

This so peeved his patron, Pope Julius II, that he often resorted to ruses to gain access to the chapel. Once when Julius believed the artist was away, he disguised himself and bribed Michelangelo's assistants, only to be greeted by planks hurled from the scaffolding above where a furious Michelangelo had lain in wait suspecting such treachery.

Five years ago, no one would have thought to embark on such a task, particularly after the painting by Raphael in the loggia of the papal audience hall restored at that time had yielded such disappointing results.

That the Sistine Chapel project came about at all was almost an accident.

As Pietrangeli explained two years ago at the start of the restoration, ''We didn't plan to restore Michelangelo's frescoes. But as the scaffolding [from cleaning the wall portraits of the early Popes] was near a lunette, we thought we might as well do a cleaning test on a small area . . . and the rest just followed.''