THIS MONTH, conductor Rafael Fru hbeck de Burgos has two full-time jobs. His schedule, posted on the wall of an office at the Washington Opera, looks a bit like a railroad time table with cryptic hand-wrriten notes (strange words like "SIN" and "CAR") to add to the confusion.

Fruhbeck is living at the Watergate these days but spending nearly all of his time at the Kennedy Center, where he has been busy with up to three rehearsals or performances, seven days a week, for the past two weeks. Mornings, he is usually rehearsing the National Symphony Orchestra -- one of his full-time jobs. Afternoons, some evenings and even an occasional morning, he has been preparing the singers ("SIN") for "Carmen" ("CAR"), which will open the opera season here next Saturday night. "In a normal week," he observed a few days ago, "I have about eight rehearsals and performances. This week, it comes to 15."

Fru hbeck is not the only one who is feverishly busy as the opera season approaches -- though he is the only one conducting a symphony orchestra with one hand and an opera company with the other. Backstage at the Opera House, three rehearsal studios are active almost around the clock, with the preparations for "Carmen," "Falstaff" (opening a week from tomorrow) and "Tosca" (opening Nov. 5). Singers from three casts wander through the backstage corridors, warming up their voices in a variety of languages; pianos in the rehearsal studios run repeatedly through the introduction to an aria while a stage director blocks out the singer's movements; technicians shift a table from one side of the room to the other, or rip up and press down pieces of colored tape on the floor to represent the scenery, with its openings for exits and entrances.

This kind of scene has been happening backstage in opera houses from Milan to San Diego this month. In the Kennedy Center Opera House, as at La Scala or the Vienna State Opera, a bewildering variety of highly specialized skills must be coordinated. Involving elements of theater (scenery, lights, costume, acting and stage direction) as well as vocal and orchestral music, pageantry and dance, opera is the most complicated of the performing arts, the most difficult and, for a rapidly growing audience, the most fascinating. Often the singers must perform effectively in languages they do not speak; the stagehands must be ready to switch from a Spanish marketplace one evening to an Italian cathedral or a tavern in Renaissance England the next. Unlike spoken theater, a contemporary opera production has two people in charge: a conductor and a stage director. They do not always agree on how it should be done, and the singers must take instructions from both.

In one Kennedy Center studio a few days ago, mezzo-soprano Martha Senn was standing by the piano absorbing a castanet lesson from flamenco dancer Anna Martinez, who will be dancing in "Carmen" and speaks no English. While the piano rippled out the Gypsy song, Senn clicked the little pieces of wood, catching the rhythm and listening carefully to Martinez's tips on fine points of technique. "Gracias, Anna," she said after the lesson, then dashed to her next session across the room -- about pacing and gestures for a flirtation scene with the toreador, baritone J. Patrick Raftery.

"I like that," said director Michael Kahn, "keep your hand on her arm just a second longer." "I'll save touching her hair until later?" asked Raftery. "Later," said Kahn. "No kisses?" asked Raftery. "No kisses in Act III," said Senn, shifting easily from sung French to spoken English. A few minutes later, Raftery was gone, and Senn was in the middle of the quintet, fending off the advances of two men simultaneously with advice from Kahn.

Meanwhile, Fru hbeck was in the Concert Hall with the NSO, immersed in a rehearsal of the Dvorak Piano Concerto. Soloist Rudolf Firkusny, in a blue turtleneck and gray slacks, swept smoothly to the end of a movement and Fru hbeck gave him a half-whispered "bravo" before turning back to the orchestra: "From bar 74--letter E," adjusting the pace and balances, polishing the tone . . . "oboe, less ta-ta-ta," and the staccato vanished from the oboe sound.

Rehearsing an orchestra is complicated, but it is part of an established, year-round routine. Preparing an opera production is enormously more complex. In an international company like the Washington Opera, a new production links with other musical events around the world, and its details must be scheduled far ahead. Among the singers in this production, for example, tenor Dennis Bailey is planning an engagement at Bayreuth after doing "Carmen" and "The Turn of the Screw" in Washington, baritone Raftery will be in Houston for "Pagliacci," in Hamburg for "The Barber of Seville" and in Chicago for "Manon" later this season, and bass Allan Glassman is preparing for his Metropolitan debut. Soprano Elizabeth Knighton, after "Turn of the Screw," will be singing Offenbach in Canada. During the current season, Michael Kahn will be directing several productions for the Kennedy Center and Broadway, including Shakespeare's "Pericles," "Showboat" and "Whodunnit." The precision needed to interlock so many complex schedules is something like assembling a jigsaw puzzle -- one with moving parts.

Martha Senn, a Colombian, is a last-minute addition to the "Carmen" cast. When Alicia Nafe' was sidelined by illness last week, Senn flew up from Bogota for an audition and hasn't flown back yet. In December, she will be doing "Tales of Hoffmann" in Connecticut and in February she will bring her Carmen to Tucson, Phoenix and Memphis, as well as singing in "Faust" in Philadelphia. It will be very surprising if she is not seen again in Washington soon.

Fru hbeck has been part of the planning for more than two years -- since the time when Martin Feinstein was directing both the opera company and the National Symphony. His schedule, as one of the leading international conductors, is busier than any singer's. He began this season with two weeks in Stockholm and after his long stay in Washington he will go to Philadelphia for two weeks, returning briefly to the Kennedy Center as guest conductor of the Philadelphia Orchestra. He will end the year in Tokyo with the annual orgy of Beethoven's Ninth Symphony that is becoming a Christmas tradition in Japan -- eight performances in a row, for which he will need two choruses and two sets of soloists.

In such a schedule, simultaneous engagements with an opera company and a symphony orchestra are only a minor challenge -- one that Fru hbeck has met before in Spain. "For a professional conductor," he says, "it should be no problem. It's all music." But it does require planning and coordination. Feinstein knew back in the late '70s that Mstislav Rostropovich would be in Paris this month, conducting the final operatic appearances of his wife, Galina Vishnevskaya, in "Eugene Onegin." This meant that Fru hbeck would be in Washington for six weeks at the beginning of the season, substituting for Rostropovich, and Feinstein saw the opportunity for a "Carmen" conducted by Fruhbeck -- his American debut in staged opera. Why not do the opera in his spare time while he was here for the symphony? At the time, Fru hbeck hesitated: "I don't want to do opera anymore." He was still upset about the stage direction of his last opera engagement, a "Carmen" in Europe. "Some people try to be original at any cost," he says, "even if it means defying the composer's intentions."

But Martin Feinstein is a very persuasive man. "After Rafael said no," he recalls, "we got into a theoretical discussion of the problems of producing 'Carmen' -- do you do it with spoken dialogue or recitatives? How would you cast it? Should there be any cuts in the music? He began to be interested in the subject, then I told him that we had Nafe'. He knows her and respects her work, and that did it; he agreed. Now, we can't have Nafe', but after Martha Senn's first rehearsal he came to me and said, 'She is a jewel.' We're already thinking about her for other roles."

As for the problem of the stage director, Kahn says in this production it is nonexistent: "I haven't done much opera, but I am one director who knows music. I listen, and the music tells when to move and when to be still and what the feeling is. The composer has put all of that into the score, and it would be silly to ignore it. Fru hbeck and I are on the same wavelength because we're both paying attention to the same music. He certainly knows the opera as well as any human being."

The only problem left then was scheduling: how to juggle a symphony orchestra and an opera company? This boiled down to a question of Fru hbeck's time, which could be budgeted, and his energy, which seems almost unlimited. The "Carmen" performances were scheduled carefully and almost successfully to avoid conflict with the National Symphony, but there was one collision that could not be avoided: Nov. 7, when "Carmen" meets "Carmina." On that Sunday afternoon, there will be simultaneous matinee performances of "Carmina Burana" by the NSO and "Carmen" by the Washington Opera -- and the NSO performance is an important one, scheduled for nationwide live broadcast under the NSO's new agreement with the Mutual Radio Network. The beneficiary of this conflict will be the NSO's associate conductor, Hugh Wolff, who picks up the baton Sunday afternoon and gets national exposure in a spectacular and popular showpiece.