"At this point, peace may be the only road to survival on this planet," Washington composer Frances Thompson McKay says in a program note to her oratorio "A Critical Mass." This complex, powerful work, which had one of its rare performances Saturday night in St. Mark's Church, Capitol Hill, is a protest against a world in which the United States spends billions on its nuclear arsenal while thousands of people die each day because of hunger.

It is also a plaintive appeal for peace. Its title has a double meaning: It is a critical look at the world using some of the concepts and structures of the Roman Catholic Mass. But critical mass is also a technical term for when nuclear material attains a self-sustaining chain reaction. The music often had an explosive quality that called to mind the second meaning.

Scored for chorus, orchestra, solo soprano, narrator, readers, gamelan and bleak computer-generated sounds evoking post-atomic disaster, the work uses different elements in each of its eight movements.

Underlying the whole structure is a long, fervent prayer for peace written by Thomas Merton, which was printed in the program and used in the performance in various ways. At one point, the narrator, the Rev. Paul Abernathy, read a substantial excerpt. At another, in some way the apex of the piece, members of the audience simultaneously read segments of it. No words emerged clearly as the voices reading different texts rose to a climax and subsided, but the impression of humanity yearning for a better world was overwhelming.

Joel Lazar conducted the performers, who included soprano Kathleen Wilson and the St. Mark's Festival Choir, with an eloquent mastery of the work's complexities.

-- Joseph McLellan