The conventional practice when a visiting orchestra tours is to avoid music not already familiar to local listeners_unfamiliar players doing unfamiliar music can mean a double burden at the box office. And conductors of touring orchestras normally want attention focused on the character of the playing, not the character of the music.

But when the Prague Symphony Orchestra performs at the Kennedy Center Friday night, conductor Jiri Belohlavek will make a bold departure from that norm. The concert -- without intermission -- will consist of an 85-minute "Dramatic Legend for Soloists, Chorus and Orchestra" called "The Specter's Bride," set to a Czech folk poem. Only the name of the composer is celebrated -- Antonin Dvorak.

For reasons that are unclear, this great composer's vocal music (including 10 considerable operas) is as little known in the United States as his orchestral and chamber music is omnipresent. One who does know the music and is very fond of it is conductor Norman Scribner, whose Choral Arts Society will sing "The Specter's Bride" (in Czech) with the Prague Symphony. Scribner describes the work as "voluptuous, melodic and passionate." It is, he adds, "heavily choral and perfectly orchestrated, more Wagnerian than usual for Dvora'k, ending in music that sounds sort of like 'Lohengrin.' "

The subject is classic 19th century: a devout maiden spirited off in the dead of night by a sinister specter, in a drama that pits her faith against the specter's temptations. A clue: Her prayers prevail.