efore James Levine took over the music directorship of the Boston Symphony Orchestra this fall, one uncomfortable question loomed: Would a conductor entering his 60's and grappling with health problems be able to reinvigorate an orchestra badly in need of fresh leadership?

New Yorkers got their first chance to hear Mr. Levine in action with the Boston Symphony at Carnegie Hall in October, when he repeated the work of his triumphant inaugural concert in Boston, Mahler's gargantuan "Symphony of a Thousand."

On Monday night Mr. Levine was back at the hall with his Boston players, as well as with the robust and impressive Tanglewood Festival Chorus and three stellar vocal soloists for a performance of Berlioz's seldom-heard "Roméo et Juliette." Mr. Levine led a rapturous, vibrant and lucid account of this unconventional, sometimes baffling yet visionary work. The orchestra sounded splendid and the players exuded involvement.

There is so much collective experience among the Boston Symphony musicians that they hardly need a kinetic maestro to whip them into action. In Mr. Levine they have something more valuable: an inspiring musician and trustworthy leader. Sitting on a conductor's stool at Carnegie Hall, hunched over the score, his gaze always on the players, never calling attention to himself with ostentatious gestures, Mr. Levine accomplished his often-stated wish to disappear into a performance in the most artistic sense.

When Berlioz composed "Roméo et Juliette" in 1839, he was enthralled with Shakespeare and driven to take the legacy of Beethoven the symphonist into the future. The ambitious work, over two hours long, is at once a seven-movement choral symphony and a dramatic cantata relating episodes from Shakespeare's tragedy of impassioned young lovers.

Throughout the performance Mr. Levine seemed intent on fleshing out the volatile drama in Berlioz's score while articulating the work's purely musical dimensions. So in the opening orchestral movement you heard the tumult of the feuding families, but also the cleanly rendered overlapping voices of a crazed orchestral fugue. In the second movement, which depicts Roméo alone, all wistful and lovesick for Juliette, Mr. Levine uncovered anticipations of Wagner and Debussy in the lapping chordal patterns and arching lyrical lines. In the stern and glorious massed choral finale, as Friar Laurence (the virile bass-baritone Julien Robbins) prayed for the dead lovers and shamed their warring families into renouncing hate, the music crested inexorably without any sense of being driven by anything so ordinary as a steady pulse.

The tenor Matthew Polenzani brought sweet sound and impish vitality to the song of Queen Mab. In the too short but pivotal solo scene for Juliette, who steps out of character to comment on Shakespeare's insights and poetic elegance, the mezzo-soprano Lorraine Hunt Lieberson sang with the melting expressivity and keen intelligence that admirers of her sublime artistry have come to count on. Carnegie Hall's auditorium loves the sound of her warm and dusky voice.

Mark the date March 28, the next Carnegie Hall concert by Mr. Levine and the Boston Symphony.