WHEN JAMES Levine was 10, he made his debut with the Cincinnati Symphony, playing Mendelssohn's Second Piano Concerto at a youth concert. So unperturbed was young Jimmy by this event that he actually neglected to tell his parents. They learned of his passage into public life only by accidentally overhearing him on the phone -- trying to decide whether his name should appear as "James" or "Jimmy" on the concert program.

Levine is now 36, and as unperturbedly self sufficient as ever. The instrument he plays these days, as music director and frequent conductor, is the Metropolitan Opera, an ensemble that arrives here tomorrow with a complement of 311 -- an orchestra of 94, a chorous of 77, a ballet of 23, with 73 principle artists, four conductors, 180 tons of equipment, 1,500 costumes, 500 pairs of shoes and 600 wigs. This will be the company's premiere engagement at the Kennedy Center, where its five offerings -- "Otello" and "A Masked Ball" by Verdi; Tchaikovsky's "Eugene Onegin," "Hansel and Gretel" and Benjamin Britten's "Billy Budd," are already sold out.

Can one man possibly feel himself really in control of the Metropolitan Opera?

"Of course not," Levine said, grinning comfortably in a plush office deep in the labyrinth of New York's Lincoln Center. "But remember," he added in wry explanation, "my responsibility is limited by contract -- I only have to worry about how it all sounds."

It is that characteristically undeterred spirit, neither blase nor compulsive, which has made Jimmy Levine, as he is universally known backstage, an instant legend in the normally frantic world of music. It hasn't hurt either that he is apparently a genius. He is the roly-poly wunderkind from cincinnati who slipped into the Met at age 27 as principal conductor, was named music director four years ago at 32, and is now one of a ruling triumvirate that has brought the grand dinosaur of grand opera up on its hind legs again.

With Wall Street lawyer Anthony A. Bliss in charge of money, and Britain's John Dexter in charge of the physical production of new works, the Met -- deep in the red in recent years -- broke into the black in 1977-78, and has remained there despite an annual budget grown now to $43 million. Critical notices for Levine's conducting there have been very favorable.

Other contrasts are equally apparent. For many years, the Met was run by Sir Rudolph Bing, a man of whom Cyril Ritchard reportedly said, "Don't be misled . . . behind that cold, austere, exterior there beats a heart of stone." The aloof Bing retired eight years ago at age 71, after 22 years as general manager. Levine conducted at his gala farewell.

Levine, however, is about as loof as you can get -- and still have 100 uncut opera scores committed to memory, a high-profile administrative and artistic position, tempermental opera singers to deal with, and four new productions a year to stage.

He can still discuss, without sentimentality or cynicism, why he likes opera.

"It's kind of hard, because of course opera is at the same time instrumental music, vocal music, drama, poetry, acting, dancing, the whole theatrical panorama of human emotions, human drama, human comedy. But that doesn't explain it. Maybe it's that there are certain kinds of music that the more you give it, the more it gives you. You finish conducting one, and you just want to start all over again."

An opera that Levine has done over and over again is Verdi's "Otello." "There's no way you're going to do that one in any single performance. Every one should be better, or at least different. If I thought mine were getting worse, I would stop. But these two "Otellos" we're doing in Washington are actually the last for four years -- we won't do that one again until the 1984-85 season. It gets a rest, and then we'll start working on it again."

It is an understatement to say that Levine likes to conduct. His fingers have to be pried off the baton just to get him out of the orchestra pit. Saturday before last, for example, he was seen on national prime-time TV conducting "Don Carlo." While that was being broadcast, he was in fact conducting live at the Met; that afternoon, he also conducted; and Monday night, he led his orchestra, chorus and singers personally through five hours of Richard Wagner's "Parsifal," which even he concedes is the most exhausting piece in the repertory. This has been pointedly pointed out occasionally in New York, where the fans like to see famous guest conductors, too.

"I'm a conductor," Levine explained patiently. "Conductors conduct. Why should I stay (at the Met) if I don't conduct? My choice is simple: I can be an absentee director, in which caase they'll say 'where is he?' Or I can stay here and conduct, and they'll say 'but he conducts too much.'

"But I must say, it's nonsense, because we try very hard to get great conductors to come in. The dollar is devalued. They have other commitments. But the invitation is open."

There have, however, been changes in the guest conductor business. In the 1960s and 1970s, it became commonplace for famous conductors to crisscross the globe, descending from the jetstream trailing clouds of glamor, and to give less and less time to their home-base institutions. Levine thinks that that era is about over, and that music will be the better for it.

"More and more of the great conductors now limit the number of organizations they work with," he said. "For example, I myself get offers from La Scala and Vienna and Covent Garden, for me to go there and conduct in the middle of winter. But we are asking ourselves, why should I live out of a suitcase? oIf I stayed home and conducted my own orchestra, the same concerts would be a building block for the future. There should be some continuum.

"In fact, I conduct about a third of the Met series. When Troscanini and Mahler and Mitropolous were at the Met, they conducted about that proportion. In recent years, every place became a sort of itinerent showcase, and everybody went everywhere within 18 months. That's bad enough for singers, but for conductors it's intrinsically ludicrous."

There is no substitute, Levine believes, for a gradual building up understanding between players, singers, designers, conductors, and even fund-raisers. "Look at George Solti, the music director of the Chicago Symphony. He is there only 12 weeks out of the year. The orchestra thinks it's not enough, and the board thinks it's not enough, the audience thinks it's not enough, and I think they're right."

Levine's own yearly schedule includes a month at Chicago's Ravinia Festival and six weeks with the Vienna Philharmonic in Salzburg, but he makes only a very few quest conducting appearances. "I guess it's a way of keeping one's image active," he said, "but I don't understand why people should be interested in their quote image unquote. It's much better to have a sustained relationship with an organization, to develop in subtle ways."

Jimmy Levine does have an image, of course. It is the image of a Nice Guy from Cincinnati who, despite a great talent and knowledge, never abuses his colleagues, seldom throws tantrums, and is in for the long haul.

On temperment:

"I frankly have never found it necessary to be abusive. Usually a talented singer will respond much more quickly just to energy and commitment. It really is possible to insist on something, even to demand it, because the music makes it important -- not some inherent ego trip. That autocratic tradition is on the way out, I think."

Levine says that he is now asked for advice by young conductors seeking to learn what works and what doesn't when one takes baton in hand.

"I tell them, look, only twice have I been asked by players I respect not to reengage a specific guest conductor. In both cases these conductors followed a common pattern. There was some kind of neurotic ego game that led them to irritate players, to be negative and abusive in rehearsal and generally self-indulgent. And in both cases there indeed were problems with the performance, and in both cases the problems were their fault.

"If you're brilliant, the orchestra will put up with it. But if you're a dilletante -- no."

Nevertheless, there have been a few crises during Levin'e tenure, and they have been operatically public. Ames McCracken, the noted tenor, quit the Met upon learning that he would not be playing 'Otello' -- his best-known role -- in the television production. Levine says he had wanted to put McCracken on Tv in Wagner's "Tannhauser," but the television deal fell through. Joan Sutherland was quoted widely as claiming to have been 'fired' in a dispute over a production of "The Merry Widow." She wanted a new production installed at the Met, in which she would sing. Levine wanted her to sing, but not in a new production of "The Merry Widow."

Levine does not brood over such things. "I never brood about anything," he said, somewhat defensively. That includes bad reviews, such as many of those drawn by "Mahagonny," the difficult cabaret-style Kurt Weill piece that the Met revived and telecast last fall, and the much reviled "The Flying Dutchman," directed by Jean-Pierre Ponnelle. "I'm prepared for some of the audience to think it's good, some lousy, and to run the whole spectrum of human nature. People assume that we're satisfied with what we put on, but ha! We're almost never satisfied. All you can hope for is a strong point of view. And that the music is not interfered with.

"It's funny, though. Ron Wilford (his manager) once said to me that I was the only person he'd ever known who was without any really fundamental conflicts. That may be true. I've always thought of myself as lucky that way. Most of the desperate deep hangups for other people are nothing to me."

His younger brother, Tom, recalling their youth together in Cincinnatti, says simple: "Jimmy was one of those people who knew what he wanted to do right from the beginning, and went and did it. A lot of the rest of us didn't even get it figured out by the time we gout out of college."

Tom Levine, a painter who also lives in New York, now asists his brother "running interference, and in some business matters," as part of a support team that also includes Sue Thomson, Jimmy's friend-in-residence at their 74th Street apartment. His parents were supportive, and Jimmy started piano lessons at age 4. In his teen-age years he commuted to New York's Juilliard School, attracted well-regarded teachers, and spent long, well remembered musical summers at Marlboro and Aspen. He polished his skills as an assistant to George Szell in Cleveland, and moved from there quickly to the Met.

Levine was never distracted by sports ("Sure, I went to baseball games, and hockey games as a kid, but I was never enthralled. I was always wishing I was somewhere else."), and he was also spared, as it happened, the urge to compose. "Oh, I took all the courses. I learned how to do it. But the thing is, I'm no good at it. I have no particular talent. So that is that."

His distractions remain few. "I like to walk, and I do a lot of it. I travel, of course. And last year I managed to reread almost all of the George Bernard Shaw plays. I go on binges like that. I'll go on a bridge binge, play every night for a week, and then not play again for four years." He has a weekend house in upstate New York, but hardly ever goes there. Though his income is said to be well into six figures, it does not translate into flamboyance in any notable way.

He is becoming well-known, however -- as Met telecasts make his frizzy mop-top hairdo and relatively subdued conducting presence increasingly known across the land. He has several times been interviewed between acts on television, and finds he likes it fine. And he is losing weight -- having joined a number of formerly larger-than-life opera notables now increasingly diminishing on a diet of television exposure.

For Levine, the future seems as carefully mapped out as his present apparently was. His five-year contract expires next year, and it seems likely he will be reengaged for another five-year term. Somewhere down the road he would like to add an orchestra for another five months of the year, leaving two months off.

"I khave a plan," he said. "What I really believe is that music is made best under a clear set of circumstances -- conductors and orchestra and chorus working closely together over a period of years, defining and deepening their rapport in different styles. I sort of hoped I might manage to do most of the music that really matters by the time I was 40.

"Then, during the second half of my life, I could do it all over again. When I'm 60, I want to have lived my life with this music. If my growth has been steady, important things will perhaps come of it."