IT WAS 4 o'clock on a Friday afternoon and, talking with James Levine in his office at the Metropolitan Opera, you would think he didn't have a care in the world. Yet in four hours he was slated to conduct the ferocious complexities of Alban Berg's "Lulu," in its first complete New York production.

Delayed by strikes of orchestra and chorus, the Met had enjoyed a pre-season opener earlier when music director Levine donned his symphonic garb to lead the Mahler Second Symphony for the first time in the history of the house. Levine, bubbling with energy and eager to talk about the upcoming season -- which will include two April weeks at the Kennedy Center -- was enthusiastic about the Mahler.

"The whole reason we did the Mahler: As a result of the strike, there wasn't the right kind of production time to do an opera and yet I needed something to rehearse the whole company together in. The only real problem we have doing concerts here is that we do it so rarely that we haven't had a proper acoustical shell for it. Now we will get one." There is a long history of doing concert works at the Met: The Verdi Requiem, which Levine will conduct in New York and in Washington in the spring, has often been done, as well as the Rossini "Stabat Mater," the Beethoven Ninth Symphony and others.

"I found an important artistic element in doing the Mahler," Levine continued. "It's very important for an orchestra and chorus that play opera all the time to play something else sometimes. The same way it's important for a symphony orchestra to play a concert 'Elektra' or 'Wozzeck.' It's important for their nervous systems' grasp of that whole repertoire. We just happened to have that opportunity because 'Lulu' had to be the first opera. There was time in the pre-season period to do something else, but we didn't have the singers or production time to do a whole opera. And I thought, 'We're doing "Lulu," we're doing "Tristan," Mahler is in the same direction.' The orchestra and chorus had never done it; and also, Mahler was once associated with the Met." (Mahler was one of the principal conductors of the Metropolitan for two seasons, sharing the podium with Toscanini.)

"Also I could rehearse the whole chorus and orchestra together. And we were facing the fact that, because the settlement came when it did, the first few operas don't put the company all together. "Lulu" has no chorus, "Tristan" has only men, "Carmelites" only women until the very end, "Hansel" has no chorus. It would not have been until "Cav and Pag" that they had anything to do together. This Mahler has turned out to be a great shot in the arm. Everyone has worked so very hard."

Levine, who has been conducting all the Mahler symphonies in recent years, proved illuminating and electrifying in the work. Marilyn Horne sang with a breathtaking beauty of tone and Kathleen Battle, remaining seated in her first, ecstatic solos, phrased and sounded angelic. It is also probable that no other opera orchestra or chorus in this country could perform the music as beautifully as the Met forces did.

Levine was also looking forward to the years ahead, with the Met's 100th anniversary due in 1983-'84.

"For this season we lost some operas for the tour and had to change some things around. We had to change 'Cosi' to 'Don Giovanni'; the 'Pique Dame' production was in a conceptual difficulty and wasn't built, but the 'Traviata' was finished. It looks as though we would be able to do the 'Cosi' as a new production this year. It looks as though the whole cast can come early enough for that. The main problem remaining is how to solve the problem of the rehearsals of the 'Ring,' and the main way out of that may be to do one less cycle -- that's next season. The rest of this season will go pretty much the way it was. We can't do 'Parsifal' -- too many lost singers. We will do 'Salome' with the title role sung by Gwyneth Jones, Josephine Barstow and Grace Bumbrey."

Question: What change does the new orchestra settlement -- with four performances a week -- make in your life?

"Actually it makes my life better. It takes a little bit of stress, which is a crucial little stress, off the orchestra. There are times when let's say we have a performance on Thursday night, a dress rehearsal Friday morning, a performance Friday night, Saturday matinee and Saturday night. If the operas are lying wrong, that could be five services in a row for the same set of horns, the same set of trumpets, which is impossible if one of those operas is Wagner or Strauss or whatever. In that sense, the new arrangement gives them a little physical relief. But it also gives me one other improvement: Because the regular members of the orchestra now play only four performances a week, it means I need a larger pool of regular extra players.

"Our system for regular extra players is that they are exactly the same as the regular members of the orchestra except that their union pay structure is different. For the Mahler I rehearsed the whole pool, all the extra strings and winds. Our system has always been, since I've been music director, that for reading rehearsals I always rehearse the entire string section for everything, and one set for winds, brass and percussion, the alternate set being used as their covers. That way everybody plays about equal, I work with everybody about equally, and when people are sick we have ready replacements. This whole word 'substitute' is completely misunderstood. People think that means you pick up somebody off the street. Not at all. It's only a contractural designation and it means that I know I have a larger pool of regular musicians to work with." A check with his secretary turned up the fact that the Met's entire pool numbers around 170 -- 93 regular, and 80 or more regular extras, which is the critical factor under the terms of the new contract.

This year Levine is conducting Lulu, Tristan, Traviata, Manon Lescaut, Mahagonny and the Verdi Requium. His schedule also allows him to guest conduct the New York Philharmonic for seven concerts in mid-January with a full calendar of concerts, operas and recordings when the Met is dark.

One of the unquenchable rumors floating around these days was that Levine would take over the direction of the Cleveland Orchestra next year when Lorin Maazel leaves to head the Vienna State Opera. He was frank about the report.

"I don't know where that stuff comes from. I talked to them about it. We talked about it early on, but I feel it's the wrong time.Not right now. I would love some day to have my own symphony orchestra but it has to be at the right time in the development of this. My contract here goes to 1986. I love the Cleveland Orchestra [Levine learned much of his conducting in Cleveland as an assistant to George Szell] and I like Cleveland. But I find I can't take a full-time symphonic responsibility while I do this the way it's organized. I love it here and the situation is exciting and stimulating and growing. And now that we have labor peace for four years, through the centennial year, I can perhaps complete this job of getting the standard we envision. Once we've got that come the questions: Do I have any more to give it? Does it have any more to give me? Do I stay longer or do I do something else? As it is now I have the music directorship at Ravinia and the recording we do there, and the time I spend at Salzburg, and I'm going to do the 100th anniversary 'Parsifal' at Bayreuth in '82. I'm doing a big festival in the Vienna Festival Weeks. The point is I need to be consolidated. I'm not a person who functions with all this. I'm going to do a series of concerts in chamber repertoire in Alice Tully Hall, and I'm still going to do another concert with [cellist] Lynn Harrell. That's all nice." Among Levine's solid accomplishments is his excellence as a pianist.

When he thinks about the Met's hundredth anniversary, Levine lights upp like a Christmas tree. "What excites me is this feeling I have, what I have always envisioned the Met to be: a place where one could see a great 'Otello,' a great 'Abduction,' 'Tannhauser' and also a great 'Lulu,' 'Mahagonny.' And when I look at our repertoire, even in this truncated season, I see our French 20th-century triple bill, I see 'Mahagonny,' 'Carmelites,' 'Lulu,' 'Manon Lescaut,' 'Don Giovanni,' 'Hansel and Gretel,' 'Tristan,' 'Salome,' 'Cav and Pag.' In other words, I see a spectrum of Wagner, Strauss, Mozart, Verdi, Puccini contemporary works. What would have been most noticeable this season, if it had gone complete, is that we have shifted the balance of the repertoire so that it is broader and doesn't rely so heavily on so many works that aren't castable in today's opera world."

Levine's remarks constantly relfect the current shortage of great voices for the more demanding operas. "In the next few years we will have new productions of 'Francesca de Rimini' and 'Il Piccolo Marat' which are important verismo works, and which are much better for us to do now than for us to do early Verdi which we don't really have the voices for in depth. Instead of doing a new 'Trovatore' where we're never going to have the depth of singers for it, we're doing a new Barber, Hoffman, Boheme, where we will have the depth of singers. When you consider how many great operas there are, and we do only 24 a year, this shift of the repertoire is possible.

"You just can't say, 'Let's do "Aida." 'I could do a marvelous 'Aida' if I only had to do three performances. But when we do 'Aida' we have to do a run and we have to do a tour and the following year."