FOR 26 YEARS, the San Francisco Mime Troupe has not only survived against all odds but also thrived as a leftist political theater collective. Not really a mime troupe, the group's Obie Award-winning shows combine guerrilla theater, commedia dell'arte, comedy and traditional drama. Original songs have become an increasingly prominent part of the mix.

"Steeltown," the group's witty and biting musical comedy currently on tour, uses a wide range of musical styles to help contrast today's sense of gloom and betrayal in American steel towns with the heady optimism in the same towns right after World War II.

The play opens in the present with Muziki Roberson singing the funky "Steeltown Blues" with a caustic edge worthy of Gil Scott- Heron. Eduardo Robledo sings "Drugs and Alcohol," a song about steelworkers' escapism, as if it were a bluesy soft-rock tune by Jimmy Buffett.

When the play shifts in the second act to 1945, a trio of Rosie the Riveters sing "The War Is Over" and "National Defense Boogie" as if they were Brechtian Andrews sisters. The harmonies sparkle and the horn section swings convincingly. Audrey Smith makes "Standin' With the Union" a raucous jump blues tune. Though the older styles prove a lot more persuasive than the more recent genres, the whole hangs together the way a musical comedy should.

SAN FRANCISCO MIME TROUPE -- "Steeltown" (Flying Fish FF347); the troupe gives three performances of "Steeltown," Friday at 8 and Saturday at 2 and 8; plus workshops (Friday from 10 to 1 and 1:30 to 4:30) at the Department of Commerce Auditorium, 14th Street between Constitution and Pennsylvania avenues NW.