To celebrate its tenth anniversary the Opera Factory is venturing out of its well-respected niche of reviving the zarzuela, Spain's national folk-operetta genre, and offering a welcome Manuel de Falla double bill. Arguably the most inventive Spanish composer of this century, Falla did dabble in the zarzuela in his youth, but it was the 1905 La vida breve ("The Short Life") that launched his career. An emotionally powerful lyrical drama rooted in populist sentimentality, the two-act opera shows Falla's innate talent at work before it was influenced by Ravel, Debussy, and other impressionists. The opera has at least one of the weaknesses of a conventional zarzuela--an implausible tragic plot about a Gypsy girl jilted by a cad--but it's distinguished by a sensuous, psychologically astute score. Semistaged, with costumes but spare sets, this production features soprano and zarzuela veteran Donna Sadlicka as the pitiable Gypsy, Raymon Cunha as her cold-hearted lover, and Paul Geiger and Debra Austin in supporting parts. Direction is by Paul Williams, a newcomer to Chicago who was affiliated with the San Antonio Opera. Philip J. Bauman conducts a chamber orchestra and the Fleur de Lys, a fledgling local chorus. As usual, the dance numbers promise to stand out; renowned flamenco specialists Pascual Olivera and Angela del Moral will be showcased in excerpts from the fiery ballet El amor brujo, also based on an Andalusian tale. Saturday, 7:30 PM, and Sunday, 3 PM, Athenaeum Theatre, 2936 N. Southport; 761-1334.