The job of conductor used to be both simpler and more dangerous. In the late 17th century, when composer Jean-Baptiste Lully conducted his “Te Deum” in a French church, the role was chiefly one of beating time for an ensemble. Lully beat it with a stick, accidentally struck his foot, and died three months later of gangrene. But timekeeping is only the most primitive aspect of an art that has grown to include the direction of all aspects of a performance, from tempo and dynamics to details of articulation, phrasing, balance, and character – not to mention, these days, programming and administration.

As early as 1739, Johann Mattheson expressed the desire not merely to direct an ensemble’s interpretation, but to bring it truly to life. It’s what we’ve come to expect. Yet only a few conductors do that in an especially spectacular way, achieving powerful results through some mysterious alchemy of technique, musical insight, and force of personality. Pianist and conductor James Levine, who brings his Boston Symphony to Carnegie Hall tonight, is certainly one of them.

Mr. Levine has, of course, been a frequent guest at that hall. As principal conductor of the Metropolitan Opera since 1973 (becoming music director in 1975 and artistic director in 1986), he forged the Met Orchestra and its chamber groups into renowned world-class ensembles in their own rights, with Carnegie Hall as their second home. He has also performed there frequently as pianist for some of the world’s leading singers in recital.

Speaking with him the other week, I wondered how it is possible for just one person to do it all. The answer quickly became clear: This is a man with a mission. His job may ultimately be, as he put it to me, simply to “communicate a composer’s work to the public.” Yet, taken with enough seriousness, this becomes a highly intricate task, one that even requires the large scale on which his career has been based.

The multiplication of the Met Opera Orchestra into both symphonic and chamber groups has been one step on the road to Mr. Levine’s goal. “It helps me more than I can describe to work with a singer and then go back to the opera house,” he said. “I would not know how to substitute for that experience. Everything we do in different sized ensembles helps us to get specific in the details of our musical performances.”

Players performing independently of the rest of the orchestra is as important as the orchestra performing without the Met’s singers. “If you are an orchestral player working on a chamber piece, you have the opportunity to experience performing outside of a large section,” Mr. Levine said. “These changes give everyone a different perspective. In recital, the specifics of character change from song to song, while in an opera you have a single character all evening. In opera, the pit can demand of you a size of expression that you don’t have when you are performing sort of in a living room.”

The end goal is not just independent recognition but better performance in the pit and the opera house as well. “I want orchestra performances to have the detail of a large chamber group. The cross-fertilization in all of these areas helps. Besides, if you are going to interpret the wishes of a composer, the more of his work you play, the closer you can get.”

His work with the Met Orchestra has contributed to James Levine’s reputation as an orchestra builder – someone who takes good ensembles and makes them great. Is there a secret? “First of all, we work very hard,” says Mr. Levine. “Second, we are not arrogant about it. This orchestra has always responded well to every attempt I made toward its development. And they have tremendous esprit des corps. I just love them, and they are still getting better.”

The program the Boston will be performing tonight – which includes works by Harbison, Stravinsky, Wuorinen, and Brahms (with Peter Serkin as piano soloist) – reflects another aspect of Mr. Levine’s approach. “Programming is something on which I spend a tremendous amount of time,” he said. “On our programs, you’ll find all kinds of relationships between the pieces, as well as very dynamic differences. This can have a big effect on the reception of a new work, and in the ability to perceive an old one in a new way.”

While rejecting the program format that was commonplace in his childhood – “the kind that had a large work on the second half and two shorter works on the first half” – he also disdains programs that are too didactic – “the audience is there to get an experience that has to do with performance, not the classroom”- or that are strung together for extra-musical reasons. More typical of his ideas are the seven concerts he gave in Munich, pairing Beethoven symphonies with the music of Arnold Schonberg.

“It changed the way the orchestra played the Beethoven,” he said, “and the way the audiences heard the Beethoven. This was exciting beyond belief. It occurred to me spontaneously one day when I was struck by similarities between pieces by both composers. I have now scheduled this for Boston in two seasons.” Presumably, the match up of contemporary music and Johannes Brahms on the Carnegie bill will provide similar insights.

Schonberg and those composers who followed in his footsteps have been an ongoing focus of Mr. Levine’s efforts. “I’m not one of these people who thinks that the Schonberg development is out of the mainstream,” he told me. “Lenny [Bernstein] would have disagreed with me. He felt that emotion comes from the harmonic implications of the diatonic scale. But if you look back, you can always find music that has all kinds of complexities and difficulties, and that was resisted at the time. People had trouble with Beethoven and with Brahms. We chuckle at this now, but if we listen to Beethoven’s Grosse Fugue, even today, we can hear things that never arose again until Schonberg.”

And Mr. Levine believes that Schonberg is one of those troubling composers whose influence, despite fickle tastes, continues to last. “What happens after a while is that the more easily digested material doesn’t remain compelling, while some of the more challenging composers are absorbed into the work of those who come later. I don’t think there has been great music since Schonberg that was not influenced by him in some way.”

As programmer-conductor Mr. Levine’s job is to allow the audience to hear these connections. “There is no doubt that continuous exposure to the difficult pieces gives audiences familiarity with them, and a way in,” he continues. “But you can’t accomplish that by force-feeding. There has to be passion and commitment on the part of the musicians, it’s the only way the audience will be served.”

Mr. Levine’s new appointment at the Boston Symphony will not, in his view, be a distraction. “Over the years, I had the thought, ‘I wonder if it will ever happen that my path will cross with a major American orchestra?’ And the offer from Boston came at a good time. I felt a strong rapport with the musicians when I’ve guest conducted. And when they approached me and learned I still had two years on my contract with the Munich Philharmonic, they were willing to wait. They wanted me, and I wanted them.

“We started at a surprisingly high level right away, and this season has been wonderful. At the same time, I’ve been working in tandem with the Met Orchestra, and it all fits perfectly. One is primarily a symphonic orchestra, and the other an opera orchestra. And now, instead of having continuous jetlag during the summers, spending so much time at European festivals like Salzburg and Bayreuth, I can focus on two places that are relatively close.”

As to rumors of health concerns, Maestro Levine can report, “I feel fine.” The benefits are all ours. Happily, he shows no signs of slowing down.

The Boston Symphony Orchestra will perform tonight at 8 p.m. (Carnegie Hall, 212- 247-7800).