Wolfgang Mozart's famous "Requiem" may be the most finished classical piece ever. Not polished, mind you, but finished.

		Mozart's 'Requiem' The Bach Choir Soloists: Maya Wirz, Jennie Blackham, Blaise Claudio Pascal, Kenneth Overton. Where & When: Trinity Cathedral, Downtown, 8 p.m. Saturday and 2 p.m. Sunday. Tickets: $10-$22; 412-394-3353. Calvary Episcopal Church Choir Soloists: Sara Botkin, Lisa Nevola, Guy Russo and Andres Cladera. Where & When: Calvary Episcopal Church, Shadyside, 7:30 p.m. Nov. 3. Tickets: Free; 412-661-0120.

Mozart died before he could complete the powerful sacred choral work. Since then, a litany of composers has done the honor, from Mozart's contemporary Franz Xaver Sussmayr (who may have talked to Mozart about it and did have the support of his widow, Constanze Mozart) to modern editors such as H. C. Robbins Landon and Robert Levin. Legends, too, supplied some additions to the work, falsely claiming that the ill Mozart died while writing it, that he secretly decided to write his own requiem and that his Viennese rival Antonio Salieri pushed Wolfgang's poor health by encouraging him to work on it. Myths all.

Over the next two weeks, two local groups are putting even more finishing touches on the moving work perhaps best known from its central role in the film "Amadeus." But the Bach Choir of Pittsburgh and the Friends of Music at Calvary Episcopal Church could hardly be more different in their treatment of the work. And both differ from the standard performing tradition of Mozart's "Requiem" as a concert work. These local groups will interpret it as a time for remembrance around All Soul's Day, Nov. 2, and in a year commemorating Mozart himself -- the 250th anniversary of his birth in Salzburg in 1756.

Calvary Episcopal will present Mozart's "Requiem" as part of the liturgical service in which these Masses for the dead were performed throughout history (a requiem Mass is essentially an elaborate funeral church service). "It is a meaningful way to experience the music in a way that the concert hall isn't," says Alan Lewis, organist and conductor. "This music is about something that is eternal in a way that a concert hall isn't. This is contemplating heaven and hell, and it is richer to experience it against a background of reading about the judgment of souls."

It's not known if the nobleman who commissioned the intended "Requiem" to be used in an actual service, but Mozart wrote it so it could. "Any Mass, requiem or not, is a set of musical movements that are part of the overall liturgical action that people attend," says Lewis.

What's missing in a concert performance are the numerous spoken elements and activities of the service, from a sermon to Communion. The Calvary performance "is interspersed with biblical readings, prayers, hymns and a recitation of a list of people that are being remembered," he says. "I think it allows the music to peak functionally as well as abstractly. It seems to be released from its laboratory and resituated in its native habitat if you do it this way."

The Bach Choir is also interspersing music between Mozart's Mass movements, but with an ear not for authenticity: opera arias, a cappella choral works and a spiritual. "I want to re-create the choral experience for the listener," says choir artistic director Thomas Douglas. "Take pieces they know and infuse them with new dramatic presentation so that audiences say, 'I never thought of it as that.' "

Douglas isn't pulling a Sussmayr and rewriting the "Requiem." "I am not trying to make any statement about how the styles of the music fit together," he says of aria insertions by Donizetti, Purcell and Mozart. But the texts of all the works he includes fit in with his interpretation of the "Requiem" as "a reflective piece for reflection and remembering." Names of people who choir members wished to have remembered will be read before and during the concert.

Douglas knows his treatment is not traditional, but he feels it gets to the "essence of the piece."

"What is this piece about?" he asks. "We can't serve the piece as a monument in a museum. It is living right now. I respect Mozart so much that I want the audience to have a new experience with him."

Finished yet again.