Choral singers have the great humdrum job in music. They dress alike, they sound alike, they drill and drill–a squad of G.I. Joes, a platoon of Unknown Soldiers. Each singer’s identity is subordinated to the needs of the group. You’re supposed to blend in. If anyone notices you, you’ve screwed up.

When Arthur Moswin tells people he’s in the Apollo Chorus of Chicago, the country’s oldest volunteer chorus and the city’s oldest musical organization, they’re usually puzzled. “I like to call us Chicago’s best kept secret,” he says, “because nobody seems to have heard of us.”

But the Apollo Chorus isn’t as obscure as Moswin says. It gets a few seconds of TV fame every Christmas, when it performs Handel’s Messiah, which it has been singing every year since 1879. Founded in 1872, the chorus predates the Chicago Symphony Orchestra by 19 years and has presented many Chicago premieres of works by great composers. The last time the Apollo Chorus gave the Chicago premiere of a work by French composer Hector Berlioz was 1887. This Saturday the group will again give the local premiere of a Berlioz work–this time a piece that until recently had been considered lost.

Berlioz composed Messe solennelle in 1824, when he was 20. He conducted it in 1825 and 1827, and then, according to his memoirs, burned the manuscript. But in 1991 a retired schoolteacher and church organist went looking for a Mozart score in a church loft in Antwerp, Belgium, and found a bound copy of Messe solennelle instead. After the score’s authenticity was verified in 1992, Messe solennelle was performed in cities around the world. Despite claiming to have burned the score, Berlioz liked parts of it well enough to use in later works.

The 200 volunteers who make up the Apollo Chorus have been rehearsing the work in the evenings in a large, spare room in the Fine Arts Building. “We have a great mix of people in the chorus,” says Moswin, who runs the HIV/AIDS clinic at Michael Reese Hospital. “We have bus drivers, teachers, students. One of our singers runs a rape crisis program in Bosnia. Sir Georg Solti’s chauffeur sings with us. He controls the music selection in the car, and every now and then he throws in one of our tapes.” The tapes must sound OK because he’s still driving Solti.

Today no one gets rich or famous composing for choruses. What was the last big choral hit? “We Are the World”? That too was the product of volunteers, but it was a bunch of soloists waiting for their turns. As choruses go, the Apollo is much better. Their names, if anyone’s interested, are in the program.

The Apollo Chorus performs Messe solennelle at 8 PM Saturday at Orchestra Hall, 220 S. Michigan; tickets cost $10 to $23. Call 708-960-2251 for reservations.