Six weeks from today the Vienna State Opera, one of the most distinguished of companies, will make its American debut at the Kennedy Center. Most performances are already sold out even though the box office will not be open for another week.

Thus tonight's three-hour gala broadcast (Channel 26 at 9 p.m., simulcast on WETA-FM) from the opera's elegant neobaroque home on the Ringstrasse may be the closest that many Washington music lovers will get to the State Opera.

Tonight's three-part concert is a tape of a Sept. 1 gala with 17 soloists singing mostly Verdi and Wagner. In the commentary, much is made of the fact that both composers conducted their own works in the handsome crimson and white interior of the house.

Neither composer, though, is part of the mainstream of the Viennese musical tradition -- represented by the composers whose works will be staged -- Mozart, Beethoven and Richard Strauss. And only four of the singers in the gala will make the trip to Washington.

The broadcast illustrates both the strengths and weaknesses of the gala format.As one well-known television producer observes, "If you invite soprano X to sing, then to keep the peace you must also invite soprano Y, even though soprano Y is less talented." The inevitable result is erratic mish-mash.

Opera performance at its best does not appear until the second hour, when bass Nicolai Ghiaurov sings and mimes a brilliant "La Calunnia" from Rossini's "The Barber of Seville." Later, baritone Piero Cappuccilli sings an intense "Nemico della patria" from Giordano's "Andrea Chenier." The biggest splash is made, however, by tenor Placido Domingo, who sings a "Chenier" aria and another from Halevy's "La Juive," then conducts Verdi's "La Forza del Distino" and also serves as host at the show's opening.