The Metropolitan Opera's much-anticipated presentation of Wagner's "Ring des Nibelungen," the first of three complete cycles, officially begins tomorrow afternoon. But it got off to an early start on Wednesday night with an extra performance of the first of the four operas, "Das Rheingold."

This is the fifth time since 1989 that the Met has presented the complete "Ring" in Otto Schenk's production. So in a way this monumental undertaking has become familiar. With several pivotal members of the cast repeating their roles, it would not have been surprising if the performance had slipped into routine, or contained a sense of a warm-up for the real thing.

Quite the opposite was true. The audience sat in rapt attention for two and a half uninterrupted hours (Wagner fans are the best behaved) through a dramatically taut and spaciously beautiful performance. And most of the credit belonged to James Levine, who conducted with an authority that comes from great experience, yet with a palpable sense of discovery as well.

During the orchestral prologue, quietly primordial music that evokes the endless flowing of time and the undulant currents of the river, it was hard to believe the amount of variety, detail and nuance that Mr. Levine drew from what are essentially 136 bars of a sustained E flat major tonality. All of the components of the music   ?   the subdued horn calls, the gently rippling figures in the violins, the tremulous drone of the prolonged pedal tones from the brass and bass   ?   were executed with lucid clarity and rich colors. Even the opera's film-scorish moments, like the grumbling, ominous, drum-thwacking music of the giants, were played with integrity as well as character.

Mr. Levine's desire to highlight the refinement and lightness in Wagner has influenced his choice of "Ring" casts over the years. It was gratifying to again hear Hei-Kyung Hong, essentially a lyric soprano, bring vulnerability and lyricism to the role of Freia, the goddess of youth. The three Rheinmaidens, Joyce Guyer, Kristine Jepson and Jane Bunnell, sang the music with full but refreshingly unforced sound. And the British tenor Philip Langridge, an artist in the mold of Peter Pears, singing with crisp diction and bright, clear tone, stole the show with his beguiling portrayal of Loge, the demigod of fire and trickery.

The stentorian bass-baritone James Morris remains a great Wotan. True, his voice has lost some of its glory; there were patches of dry tone and rough legato. But he still vocalizes the role better than anyone else singing it today, and his poignant portrayal of the brooding god just gets richer.

The soprano Hanna Schwarz, returning to the role of Fricka, Wotan's wife, had moments of dicey pitch and edgy tone. But over all her singing was radiant, distinguished and affecting. The baritone Ekkehard Wlaschiha brought his keen skills as a character actor to the role of Alberich the dwarf. Though his singing often had an approximate relationship to the pitches in Wagner's score, his booming nasal sound was just right for the scheming Nibelung.

The basses Eric Halfvarson and Sergei Koptchak, as the giants Fasolt and Fafner, were vocally powerful and unusually sympathetic   ?   big, sad, lumbering creatures with world-weary voices. There were strong performances from the tenors Mark Baker as Froh and Alan Held as Donner, and from the mezzo-soprano Birgitta Svenden as the earth goddess Erda.

Mr. Schenk's production, a realistic "Das Rheingold" that recalls the illustrations in the old "Victor Book of the Opera," has been much debated over the years. It looks very familiar now, and a bit dusty. But the musical performance was utterly fresh.