The world's second-oldest contemporary art exhibition, the 51st Carnegie International, will feature 40 artists this year, including 80-year-old avant-garde composer John Cage.

The 1991 show will spill from the formal galleries of The Carnegie Museum of Art into parks and city museums, including the Mattress Factory.The exhibition has claimed to show the best of the world's art, but the number of works included has been smaller in recent years. This year's event is scheduled to open Oct. 15 and close Feb. 15, 1992.

Only the Venice Biennale is older than the International, which is held every three years. Those two shows and the Documenta in Kassel, Germany, are said to be alone in their class.

Besides Cage, other artists invited to the International include photographer Richard Avedon, Christian Boltanski of France, Ilya Kabakov of the Soviet Union, Reinhard Mucha of Germany and Maria Nordman of the United States.