Hector Berlioz is probably the most misunderstood of the great composers. He is best known for one of his least representative pieces, the early "Symphonie Fantastique," which typecast him as a disheveled, opium-munching romantic who channeled his hallucinations into music. (Indeed, the scholar Jacques Barzun went so far as to title his two-volume biography "Berlioz and the Romantic Century.")

And yet the composer's operatic masterpiece, "Les Troyens," which returned to the Metropolitan Opera repertory on Monday night, presents a very different Berlioz. This five-act, four-hour pageant of dance and music drama, first performed in 1890, is shot through with a chaste, high-minded nobility that is like nothing else in the repertory. It is, I suppose, a "radical" work in many ways -- certainly some of the harmonies in "Les Troyens" would not become commonplace for the better part of a century after it was written -- but, gloriously, it looks backward for inspiration, to the writings of Homer and Virgil, to the stoicism of ancient Rome, to the timeless values of the classical.

It is instructive to note that this was only the 29th performance of "Les Troyens" in the Met's history, while many lesser operas long ago passed the 500 mark. There are a number of reasons for this. To begin with, for more than a century after "Les Troyens" was finished, the score lay about as a set of mysterious fragments (a little like the latter-day Forum or Colosseum). Even after the landmark performing edition was assembled in 1969, the opera's size and complexity scared off most presenters. For many years, "Les Troyens" survived only as a sort of glorious rumor -- the great French Grand Opera that nobody had heard.

The Met staged "Les Troyens" for the first time in 1973. That production was very much of its time -- imagine the city of Troy as psychedelic leather disco -- but it attracted many fine singers, and it was brought back in 1983 and 1993. Now Francesca Zambello has supervised a new production, one that combines a coolly austere modernist design with panoramic activity from a huge cast.

I think the current staging will do handily once some of the present busyness is toned down: Right now, the profligate employment of people and props reminds me of the meaningless activity Samuel Johnson once dismissed as "mounting a horse in the middle of a sea voyage." We don't need so many extras; we don't need an onstage conductor leading the hymn to Dido as if he were a tidy church chorus master; we certainly don't need a riot of peasantry making faces and waving flags at the audience a{grv} la "Les Miz." In fact we don't need any staging at all for the "Royal Hunt and Storm": No director could possibly come up with images to match the ones Berlioz lets free in our minds during that extraordinary interlude, and the "Peter Pan"-like dancers on high wires that Zambello gives us don't begin to pass muster.

The cast is a wonderful one -- the Met at its finest. As Aeneas, tenor Ben Heppner brings an aching sensitivity to music that is too often blasted out heedlessly. Even in the most herculean passages, his interpretation was characterized by pure and unfettered songfulness. His voice broke briefly on two occasions, but he recovered immediately, and such passing technical flaws could not long detract from his general magnificence.

No less fine was soprano Lorraine Hunt Lieberson as Dido. At the beginning, I wondered whether she would have the stamina for the taxing role: Her voice sounded so sweet, pure and -- well, a size too small. But she moved from strength to strength as the evening progressed and, whether hymning ecstatically in the radiant love duet or thundering down the furies of the heavens in the finale, she met every one of Berlioz's demands while still retaining a pristine and haunting vocal luster.

Deborah Voigt brought brilliance of tone and a palpable animal anxiety to the role of Cassandra, whose fate it is to see the nightmare future looming, only to be mocked and harassed for her clarity of mind. Dwayne Croft made an ardent, dapper Coroebus; Matthew Polenzani sang the role of Iopas with delicacy and feeling; and Gregory Turay made much of Hylas's lonely song as he rode across the stage in the topsail of a doomed ship (one of Zambello's most apt touches). I was less happy with Elena Zaremba's urgent, overblown portrayal of Anna, which would have fit more appropriately into an early-20th-century Italian melodrama. There was worthy support from Robert Lloyd as Narbal, Jossie Perez as Ascanius, Julien Robbins as Priam, Jane Bunnell as Hecuba and Alexandra Deshorties in the silent role of Andromache (the character is represented musically by a disconsolate clarinet).

James Levine led the Metropolitan Opera Orchestra and Chorus in a clarified, meticulously structured performance, one that stressed Berlioz's classicism and composure. Still, again and again, the opera transcends its conservative roots to soar into absolute unpredictability. The music that accompanies the death of Laocoon is almost unbearable in its intensity, while I should be hard-pressed to imagine anything more achingly beautiful than the last hour of Act 4 -- a succession of miracles. This is great opera on every level. There will be several more performances (beginning on Friday) and a nationwide radio broadcast on Feb. 22.

Ben Heppner as Aeneas in the Metropolitan Opera production.Trojan hero Aeneas (Ben Heppner) sings with Dido (Lorraine Hunt Lieberson) at the Met.The opera transcends its conservative roots to soar into absolute unpredictability.