SACRED MONSTER.

The artist who strives to create a work of everlasting genius faces many obstacles these days, not least a lack of popular demand. In the end, however, nothing stands in the way of immortality but a lack of mad ambition. Olivier Messiaen's "St. Francis of Assisi," the grandest grand opera since Wagner's "Parsifal," came into being in 1983, during the first Reagan Administration, when Men at Work topped the pop charts. Somehow, it has already acquired a historical aura, as if it were an antiquity whose head and paws are only now emerging from the sand. "St. Francis" may have to wait a century or two before it finds its proper public, but a few brave opera houses are venturing to stage it, and the history books should reward them. The heroic new production at the San Francisco Opera will probably be remembered long after the entire current season at the Met is forgotten.

"St. Francis" is not easy listening. It is five hours long, devoutly Catholic in content, and by turns dissonant, jubilant, voluptuous, and austere. There are eight tableaux, each recording a stage in the life of the saint. Francis kisses a leper, speaks to the birds, receives the stigmata, dies in a state of suffering joy. The libretto, which Messiaen wrote himself, would have posed no problems for an audience of fourteenth-century Loire villagers. The music is something else again: a twentieth-century echo chamber in which prosaic turns of phrase acquire shattering overtones. The composer once remarked that he saw the Resurrection as an atomic explosion; likewise, his Francis has to undergo a death that sounds like the apocalypse. Sitting through the opera is at times a physical challenge--even Wagner knew better than to write a two-hour second act--yet the experience leaves one feeling strangely liberated. It harks back to one of those archaic Christian liturgies in which spells of boredom give way to precisely staged epiphanies--as when, in the Greek Orthodox Easter service, the church goes dark and the light of a single candle remains.

Messiaen's great epiphany occurs in the fifth tableau, in which Francis meets a Musician Angel on the road. The episode is taken from Franciscan hagiography, according to which the friar once fainted after hearing an angel play a viol. He told his brethren, "If the Angel had played one more note--if, after down-bowing, it had made an up-bow--from unbearable sweetness my soul would have left my body." In Messiaen's version, the Angel prefaces his concert with lines borrowed from St. Thomas Aquinas: "God dazzles us by an excess of truth. Music carries us to God in default of truth." The strings play a soft, unceasing C-major chord; over it, three ondes martenot--antique electronic instruments with eerie, piercing voices--unwind a thread of melody that touches on ten of the twelve chromatic notes. As you listen, your ears are teased by two textures of sound: warm strings spreading out from the center; electronic tones pinging everywhere. At the same time, you try to reconcile the stasis of the chord and the drift of the theme. These tensions are not resolved; instead, they mark out an almost visible space, in which you may well catch a glimpse of whatever it is you consider divine. The San Francisco staging heightened the moment by creating one of the most striking tableaux in recent memory: Willard White, as Francis, lying on the ground, his body racked in ecstasy; Laura Aikin, as the Angel, dancing slowly in midair; and, at the end, ciphers from a medieval parchment materializing on a scrim. "My God," someone behind me whispered.

The angel responsible for this quasi-miraculous evening is Pamela Rosenberg, the new general director of the San Francisco Opera. A veteran of the lively, sometimes demented European opera scene, Rosenberg wants to confront a much more conservative American public with something other than the usual picture-postcard Puccini. San Francisco ...