In the 1960s, Lee Bontecou was heralded as one of the most important young artists of her time. Painstakingly crafted from castoffs--Army surplus and canvas conveyor belts from a neighboring laundry--her wall reliefs evoked a fearsome sci-fi world, a mysterious doom-filled terrain no one had ever seen before. In the mid-'70s, however, Bontecou disappeared from the art scene, declining to take part in exhibitions. Now, her work, including recent pieces, is the focus of an exhibit opening Saturday at the Museum of Contemporary Art, the first in which Bontecou's later works have been available for public comparison to her earlier pieces. The exhibit runs through May 30, 2004.