The opera isn't over until the fat lady scratches.

When the season closed, members of the San Francisco Opera were still scratching and clawing like jealous sopranos - all because of microscopic scabies mites, which had infested the backstage areas of the 62-year-old opera house. Dozens of performers came down with the itchy affliction - including, some say, one of the stars of "Lucia di Lammermoor."Finally opera executives brought out the big guns - chemical sprays, fumigants and a giant orange vacuum cleaner designed to fight mites. The backstage area and hundreds of costumes were treated.

Meanwhile, about 200 members of the opera company, including the entire orchestra, chorus and backstage crew, were given prescriptions for an anti-scabies lotion. They were instructed to smear the goop over their bodies and let the stuff remain for 10 hours.

During the outbreak, musicians taped nasty-looking drawings of the eight-legged bug throughout the backstage area, hoping management would get the message. Other wags posted a list of "possible additions to the repertoire" on the bulletin board. The list included "A Little Mite Music," "Cosi Fan Cootie," and "A Midsummer Mite's Cream."

In recent days, after what some musicians said amounted to stalling by management, opera executives consulted staff doctors, the San Francisco Health Department and a Pacific Heights dermatologist. About a dozen old sofas, upholstered chairs and rugs believed to be sources of transmission were thrown out. "They were big, old dirty brown sofas that were pretty hideous, anyway," said opera spokesman Doug Allan. "They were long overdue to be thrown out."

Allan stressed that only opera company members have suffered from scabies and that the public has not been afflicted.

Some musicians were reluctant to talk about the problem because a scabies scare could hurt the perpetually cash-strapped operation.

"No one wants to start a panic," said a violinist. "We want the critters to succumb quietly."

With any luck, millions of mites died backstage of poison as the opera conducted its final week of the season, featuring "Mefistofele," a suitably bloody tale of poisoning, drowning, death and damnation.