Leonard Bernstein's "MASS" won't append "appeal" to its name anytime soon. But despite its controversial nature and its eclectic makeup, it continues to garner performances across the world. Since 2000, at least 75 performances of the work in its full or chamber version have been given. The Bach Choir of Pittsburgh will add to that number this weekend when it performs the work at Carnegie Mellon's Chosky Theatre with the Greer Reed and Company Dance Ensemble, Children's Festival Chorus and the Academy Chamber Orchestra.

Associated Press Leonard Bernstein said of his piece, "I've not written a Mass, I've written a theater piece about a Mass." Bach Choir of Pittsburgh Bernstein's 'MASS' Featuring: Thomas Douglas, conductor; Henry O'Neill, tenor; Children's Festival Chorus; Greer Reed and Company and the Academy Chamber Orchestra. Where: Chosky Theatre on the Carnegie Mellon campus. When: 8 p.m. Saturday; 4 p.m. Sunday. Tickets: $10-$22. 412-394-3353. Listen In: Hear excerpts from the original recording of "MASS": "A Simple Song" "Gloria in Excelsis" "Meditation 1"

"Staged" actually is a better word than "performed." "I've not written a Mass, I've written a theater piece about a Mass," Bernstein once said about the work that premiered in 1971. Commissioned for the opening of the Kennedy Center in Washington, D.C., it is a semi-staged event that takes the form of the pre-Vatican II Latin Mass to pose questions about the role of the church in a time abounding with crises of faith.

Subtitled "A Theater Piece for Singers, Players, and Dancers," the work, "follows the liturgy exactly, but it is juxtaposed against frequent interruptions and commentaries ... much like a running debate," writes Nina Bernstein, the composer's daughter, on www.leonardbernstein.com.

"The hour-and-a-half-long piece relates the drama of a Celebrant whose faith is simple and pure at first, but gradually becomes unsustainable under the weight of human misery, corruption, and the trappings of his own power."

To showcase a world in need of a return to holiness, Bernstein and lyricist (and Carnegie Mellon alumnus) Stephen Schwartz used cutting theatrical elements and language. At one point, the chorus responds to a preacher saying, "And it was good, brother" with "And it was godda -- good." At another, a member of the imaginary congregation exclaims, "I'll believe in twenty gods, if they'll believe in me." But the most prominent blasphemous act comes when the Celebrant, a Christ figure disgusted by the self-centered congregation, shatters the vessels of the sacrament onto the ground.

"It was controversial," says Margaret Carson, the late Bernstein's press agent. "The only critic at the time of the opening who gave it a good review was Paul Hume of the Washington Post. Cincinnati was the first place it was performed outside of Washington. Before the performance, the archbishop issued a pastoral letter condemning it."

Since then the Catholic Church has shown acceptance of the piece. In 2000, "MASS" was even staged at the Vatican. However, controversy still follows it.

"Some people have left the choir, two specifically because they thought it was sacrilegious," says Thomas Wesley Douglas, artistic director of the Bach Choir. "I did have to spend one rehearsal talking about the piece and saying how do we as artists respond to controversial material. I don't mind people having different points of view, but there can be a point where you impede the progress of putting something out there to let people decide for themselves."

Bernstein advocates feel that the debate around "MASS" stems from a misunderstanding of the piece's use of sacrilegious elements in order to show their need for coming closer to God.

"The whole point is that it was about the crisis of faith," says Craig Urquhart, spokesman for the Bernstein Estate. "In a dramatic work there needs to be controversy. One needs to look at the final message of the work, which is all about renewal of faith and respect of faith."

"To me, the smashing of the chalice is a mirror of Jesus Christ in the Temple smashing the money-changing tables," says Douglas. "And that's when the reconciliation begins."

To others, some beliefs should simply never be used as a means to an end.

"I think it is perfectly fine for the Bach Choir to do this piece and for it to be in the repertory," says Jane Ann Thompson of Mt. Lebanon, one of the half-dozen members of the group who pulled out of the performance of "MASS."

"This is not an issue of censorship," she says. "But I received a strong conviction that I personally should not sing the piece. I certainly sing secular music that has no reference to God, but ["MASS"] is a piece about God that fails to glorify God, and that is where I draw that line."

Another criticism of the work over the years has been that a non-Catholic (Bernstein was Jewish) was being critical of the Catholic Church. But his defenders point out that "MASS" is not a diatribe against the concept of God or church, but of society's failure to listen to either. "He was a very religious man," says Carson.

Bernstein himself said in the program notes to the premiere that he intended, "to communicate as directly and universally as I can a reaffirmation of faith."

While not as controversial, "MASS" also divides listeners on its eclectic use of musical styles: rock, jazz, blues, marching band, Broadway, hymns and opera. That kind of eclecticism is typical today, but it was innovative at the time, as was the use of taped material that appears throughout (originally quadraphonically).

"Bernstein said he felt like this work was a real culmination of who he was at the time," says Douglas. "There is a little bit of everything in it. It has a different kind of appeal than listening to a Beethoven symphony, it is going to have a wider appeal." Individual movements are commonly extracted for performance, usually the "Meditations" or "A Simple Song."

It's still a bit discombobulating for some to hear a score switch so quickly from genre to genre, but for many it lends "MASS" an admirable freshness, especially as William Bolcom and other composers have since used the approach. Certainly the case could be made that the text still speaks to America, also dealing with a controversial war abroad, economic uncertainty and distrust of government.

"It is part of the genius of it that "MASS" still has some application," says Thomas. "It is universal and about humankind, sadly in some ways. It still remains very pertinent; this sounds like now."