The Chicago Symphony Orchestra will give Elliott Carter's first opera, What Next?, its American premiere this weekend--only a couple months after its composer's 91st birthday. By his own admission, Carter was a late bloomer, but it's a little puzzling that the senior statesman of American music waited so long to tackle opera. After all, he clearly thinks of music as drama: though he spent his 20s and 30s dabbling in everything from French neoclassicism to populist expressionism, he announced his mature style with String Quartet no. 1 (1951), which is dense with intricate, precisely woven textures and layers of contrasting "characters"; he's since referred to many of his scores as "auditory scenarios for the players to act out with their instruments." He's no stranger to the theater, either, having composed ballet and incidental music back in the 30s; nor does he lack a flair for vocal music, as he demonstrated in the 70s with a sparkling setting of Elizabeth Bishop's poetry. But whatever the reason for his long delay, it ended five years ago, when CSO maestro Daniel Barenboim asked him to write an opera for the Staatsoper Berlin. Carter enlisted Paul Griffiths, a new-music maven and reviewer for the New York Times, as librettist, and they settled on a scenario suggested by Jacques Tati's 1971 film Traffic: a violent car crash segues into a playful round of soul-searching by the six characters involved, five adults and a young boy. Though some of Carter's works have come across as mind games--he admits to a fondness for "streams of different things going on together," for knotty schematics and complex polyphonies--he's also professed admiration for the manic, earthy comedy of Verdi's Falstaff. If What Next? is as inspired and humanistic, it could prove a crowning achievement for Carter, whose stature in 20th-century music already rivals Verdi's reputation in the world of opera. Barenboim conducts the CSO and the cast that sang at the opera's world premiere last September in Berlin; this is a concert presentation, without sets or costumes. The second half of the program is the music from Manuel de Falla's ballet The Three-Cornered Hat. Thursday, February 24, through Saturday, February 26, 8 PM, and Tuesday, February 29, 7:30 PM, Orchestra Hall, Symphony Center, 220 S. Michigan; 312-294-3000 or 800-223-7114.