For the next few months, the agenda is sex and violence in the Opera House followed by sex and comic complications in the Terrace Theater. Two men will die repeatedly in duels, downstairs at the Kennedy Center, this month and next. Another will be assassinated by conspirators and a fourth will be dragged, alive and screaming, down to hell.

It sounds a little bit like what has been happening recently to the Washington Opera, sponsor of the above-mentioned colorful activities.

Plagued by budget problems that have forced it to cut back its 1985-86 season, the Washington Opera has also been hit by illness in two of its upcoming productions.

"Don Giovanni," coproduced with L'Orchestre de Paris, was scheduled to be conducted by Daniel Barenboim when it opens the season on Saturday night. But Barenboim contracted an ear infection that makes him unable to fly, and the company spent several days frantically searching for a replacement. Finally, John Mauceri rearranged his schedule at Covent Garden and flew in on Thursday night to begin rehearsals. To make things more complicated, the company was, at last report, still seeking a replacement for Hungarian soprano Sylvia Sass, who was scheduled to sing the leading role of Emilia in "Un Ballo in Maschera," beginning Nov. 9. So far, no problems have been reported for "Eugene Onegin," which opens Nov. 2.

Prospects look less hectic for the season in the Terrace, but that is still months away, running (sadly shortened) from late December through early February. The problem in the Terrace is that there are only two productions, Offenbach's "Christopher Columbus" (opening Dec. 28) and Donizetti's "The Daughter of the Regiment" (opening Jan. 4), where, in past years, there have been four.

The Washington Opera has taken a step backward economically this season. The high performance and production standards of recent seasons may be maintained, despite both chronic and last-minute problems. But there will be only 47 performances of five productions, compared with last year's 72 performances of seven productions. This relative austerity will also extend to the sets and costumes, but not in ways that will be very conspicuous.

Martin Feinstein, the company's general director, speaks of "four new productions," and the claim is not inaccurate if properly defined. But only one of the five, "The Daughter of the Regiment," will be a full-fledged virgin, revealed to the world for the first time when it opens in the Terrace.

The other four have been seen before, in Washington or elsewhere. "Don Giovanni" has already been given in Paris. The sets and costumes for "Eugene Onegin" are owned by the Lyric Opera of Chicago and were recently seen in a a PBS telecast from Chicago. "Christopher Columbus" has not, strictly speaking, been presented before by the Washington Opera. But it is a coproduction with the Opera Theatre of St. Louis and was seen in the Terrace in 1979 during the one short, brilliant season of the Kennedy Center Summer Opera -- an ad hoc company instigated by Feinstein to demonstrate the operatic potentials of the Terrace Theater. The characteristics of that company have since been transplanted into the Washington Opera's Terrace season, and this production is likely to resemble the one seen in 1979. For one thing, Elaine Bonazzi will be returning in the role of Queen Isabella. But nobody who saw her hilarious performance the last time is likely to complain about that.

The one production Feinstein does not describe as "new" (meaning new to the Washington Opera) is Verdi's "Un Ballo in Maschera," with the lavish sets and costumes by Zack Brown that will be well remembered from their first appearance here in 1980.

The company's cutback, a result of its spectacular, expensive and successful effort to establish itself on the international scene in recent years, has unfortunately hit it where it hurts the most. The two canceled productions would have been in the Terrace, where the Washington Opera does its most distinctive work and maintains its consistently highest standards.

When Washington Opera productions begin to appear on television (as they certainly should), the Terrace productions are the most likely to make that important breakthrough. Conceived for the intimate environment of a house that seats fewer than 500, they are designed with the qualities most essential for the close-up approach of television.

Ironically, the Terrace season was not cut back because of artistic problems or lack of audience support, but because it was still fluid when the financial crunch hit, while the Opera House season had already been locked in. The 29 performances planned for the Terrace this season sold out almost completely on subscription shortly after sales began. Single tickets are still available only for a few week-night Terrace performances, while none of the 18 performances for the three Opera House productions is listed as sold out.

The Terrace problem, fortunately, is temporary. The Morris and Gwendolyn Cafritz Foundation has given the Washington Opera a special grant of $200,000 to underwrite "Don Giovanni" and assure the restoration of a four-production season in the Terrace in 1986-87. This will not take care of the (undisclosed) total shortfall, according to development manager Lois Clark, but it puts the company within striking distance.

"We are going to other sources," says Clark, "and we can tell them that the Cafritz Foundation is so impressed with our Terrace productions that it has offered this support. That should attract sufficient funds to restore our full Terrace season. And we are looking ahead to a balanced budget in the very near future."

Even with the loss of Sylvia Sass, the upcoming season offers a number of new faces for Washington Opera patrons as well as the return of many familiar favorites. In the title role of "Don Giovanni" will be Renato Bruson, who is being hailed by some opera-lovers as the next Sherrill Milnes, and the role of Tatiana in "Eugene Onegin" will be taken by the spectacular young soprano Hei-Kyung Hong, who won wild applause last year at her Metropolitan Opera debut in "La Clemenza di Tito." Connoisseur magazine reported that "the radiant newcomer's warmly blended tone and poised phrasing had a packed house under her spell." Other singers with solidly established international reputations include Karita Mattila, Claudio Desderi, Philip Langridge, Franco Bonisoli and Juan Pons.

Baritone J. Patrick Raftery, a Washington native who made a smash hit here in the title role of "The Barber of Seville" a few years ago, repeated that triumph last season at the Paris Opera. He will be back this season in the title role of "Eugene Onegin," which could hardly contrast more sharply except in the vocal range it requires.

Other Washington favorites who will be returning include tenor Jerry Hadley as Lensky in "Eugene Onegin," Faith Esham as Zerlina in "Don Giovanni," Stephen Saxon in "Un Ballo in Maschera," John Fiorito in "Christopher Columbus" and Erie Mills and Franc,ois Loup in "The Daughter of the Regiment." Washington residents Stephen Dupont, Christopher King and Gordon Hawkins will all have roles in "Un Ballo in Maschera."