Opera SW, the feisty nonprofit opera company that for the last five years has been performing at the Westminster Presbyterian Church in Southwest Washington, is moving toward the city's center and changing its name to Opera DC. For the 1985-86 season, Opera DC will occupy Carroll Hall, a small theater owned by St. Patrick's church, at 10th and G streets NW.

The chamber opera company, founded in 1980, will present its season premiere, "The Barber of Seville," starting tomorrow in the historic theater, which was built in 1906 and was briefly a commercial theater where the likes of Kate Smith and Helen Hayes once trod the boards. Until May the building served as a gymnasium for the St. Patrick's Academy School for Girls.

Though the orchestra seating area was ripped out to make way for a gymnasium floor, the stage is intact.

"We just can't believe a stage like this exists in the middle of town," said Opera DC stage director Muriel Roberts, who just returned from a summer directing job at the University of Minnesota's Opera Institute.

"We founded Opera SW to provide the Washington area with quality chamber opera, in English, at affordable prices, using local singers," said Roberts. And that effort has been "so far, so good."

The second season production, which the company traditionally dedicates to contemporary, lesser known works, will feature Henry Mollicone's "Face on the Barroom Floor" and "Emperor Norton." Kurt Weill's "Lost in the Stars" -- a story that takes place in South Africa, and concerns a black minister's son who is falsely convicted of killing a white man -- closes the season.'