Michelangelo is on the verge of being rediscovered.

Since June 16, 1980, a team of art scholars and technicians has been methodically and delicately scraping away layers of dust and grime that have accumulated on the 400-year-old frescoes covering the ceiling and walls of the Sistine Chapel.

Their work has revealed a startling discovery: Michelangelo originally used bold, vibrant colors instead of the muted brownish tones familiar to the millions of visitors to the Sistine Chapel for centuries.

"A new Michelangelo appears in these bright colors," said Walter Persegati, secretary general of the Vatican Museums, at a news conference in New York today. "After the cleaning is complete, the evaluation of Michelangelo as a painter will have to be rewritten."

For years, art critics have said that Michelangelo simply transferred the images he envisioned as a sculptor to his paintings. But Kathleen Weil-Garris Brandt, a professor of fine arts at New York University and a leading scholar of Renaissance art, told reporters that that reputation is about to change.

"The cleaning of the chapel has completely reversed our idea of Michelangelo's contribution to the art world," she said. "He called himself a sculptor. But now that we see the colors we find he was a man who also thought like a painter. He was a painter's painter and one of the most revolutionary colorists in the whole history of art."

The chapel project, sponsored by the Vatican Museums and scheduled to be completed in 1992, involves cleaning and conservation of a 13,000-square-foot surface area that includes the ceiling, the 14 crescent-shaped areas over the windows known as the "lunettes" and the last fresco over the altar, "The Last Judgment."

Michelangelo began painting the frescoes on the ceiling and the lunettes on wet plaster in 1508, finishing the project four years later.

Work on "The Last Judgment" began in 1535 and ended six years later.

It took four years to clean the lunettes and the chapel's upper walls. Persegati revealed today that work on the chapel's ceiling, where some of Michelangelo's best-known works are located, has begun.

The new light cast on Michelangelo's work with the uncovering of his use of brilliant colors may be the most overwhelming of the restoration project's discoveries, but it is by no means the only one.

Fabrizio Mancinelli, project director, also was able to reconstruct the scaffolding used by Michelangelo, finding that it was a structure that neither touched the floor nor the ceiling of the chapel. The holes Michelangelo used to support his wooden work platform were found and used to brace a scaffolding of steel beams.

Another scholar, John Shearman of Princeton University, discovered that the ceiling had already been decorated before Pope Julius II commissioned Michelangelo to paint his frescoes in 1508. The ceiling had cracked, and iron chains had been stretched above the vault to hold it together, ruining the surface and the old decorations in the process.

"This reveals the great buckled landscape of irregularities that Michelangelo had to deal with," said Brandt.

Finally, the cleaning of the frescoes revealed a previously obscured portrait of David slaying Goliath, which on closer examination has been found to be a self-portrait of the artist.

"It David looks like the face of a figure painted by Raphael which is believed to be a portrait of Michelangelo," said Brandt, who discovered the portrait.

All of these findings will be discussed in detail at a conference Monday at the Metropolitan Museum of Art. Close to 750 art scholars and historians are expected to attend the event sponsored by the Wethersfield Institute, a group committed to the study of Christian culture through philosophy, art history, and archaeology.

A 37-minute documentary, spliced together from rolls of film taken by the Japanese Nippon Television Network, which has bought exclusive photo and television rights to the project for $3 million, also will be shown. It outlines in extensive detail the painstaking and scientific process of restoring such a monumental work.

Layers of dirt as well as the soot from the candle smoke and thick strokes of glue and paint from earlier restoration attempts have to be carefully sponged off with distilled water and chemically predetermined solvents.

The darkened somber figures that were barely discernible from the floor of the chapel 60 feet below suddenly have become bold, clear images. New details -- the lace hem of a gown, for example -- have emerged from beneath layers of centuries-old grime.

In addition to cleaning the frescoes, the project involves installing lighting systems and climate controls that track air movements, temperature and humidity to preserve the frescoes in the future.