The posters promised a rock concert, but the crowd at the door seems dressed for a high school pep club meeting. There are no studded leather jackets. No bleached Madonna hair. None of the usual Heavy Metal rock fan bravado. Tonight we're talking Topsiders, polo shirts and outfits off the Gap rack. We're talking Clean Cut.

Inside, though, all the courteous calm vanishes with the houselights when the main act hits the stage. The aisles fill faster than a rush-hour bus, the bandstand comes under siege, and for the next two hours the crowd keeps to its feet, singing along with all the songs as if they were Top 40 hits. So goes the first Carnegie Hall concert of the Violent Femmes, favorite cult band of thinking teens.

Violent Femmes? "It was just something that came out of my mouth, like automatic writing," says bass player Brian Ritchie, 25, who named the group in 1981. "We thought of the band as a temporary thing. We didn't think we'd get stuck with the name."

If all it took was an offbeat name to find success, Ritchie and Femmes drummer Victor De Lorenzo, 31, might still be playing for their old group, Hitler's Missing Testis. With the Femmes, it's music, not their label, that sets them apart. The Milwaukee trio, which features Gordon Gano, 23, on guitar, gives its mostly teenage audience a mix of rock, folk, country, gospel and hints of jazz. The group's lyrics, written by Gano and propelled by his often-anguished voice, cover enough turf to keep even brainy high school types tuned in: from adolescent angst to anti-Reagan politics ("Old mother Reagan and her crew/ Took away from me and you"). There are happy echoes of Buddy Holly in I Held Her in My Arms, darker visions of family homicide in Country Death Song("Come, little daughter, I will carry a lantern/ We'll go out tonight, we'll go to the caverns"). Gano, son of a Baptist minister, even ventures into spiritual territory where rockers seldom travel with songs like Faith and Jesus Walking on the Water. "There is something in their music you just don't hear every day," says fan Aaron Bennett, 17. "There's always something happening."

A 1983 debut album, Violent Femmes, conquered the critics but not the charts. Still, cutting-edge choreographer Mark Morris began dancing to their songs, and eventually Talking Heads keyboardist Jerry Harrison, a fellow Milwaukeean, signed on to produce their latest LP, The Blind Leading the Naked, released last February. "I thought I could help polish them," says Harrison, "help them reach beyond their original audience without taking the guts out of their music."

It wasn't polish so much as word of mouth—and their discovery by college radio stations—that began spreading the Femmes' good name outside of Milwaukee. De Lorenzo, their hyperkinetic percussion man, had come to town in 1976 to attend the University of Wisconsin and stuck around afterward to join a local theater group. Ritchie, their gangly bass player, was a native, and Gano had grown up in the suburbs. During high school there he had been both an honors student and a campus eccentric known for wearing a bathrobe to class.

That remains his costume of choice onstage. "You wouldn't say they dress cool," concedes Joe Baumgart, 16, a hometown follower. "They look more like a bowling team. I think that's neat." So do others. "We haven't let the record company pick our hairdressers," says Ritchie. "We're individuals. I think the kids look at us and realize we're not that different from them."

Since banding together, Ritchie and De Lorenzo have become husbands and fathers. The former has a year-old son; his drummer-partner, a son and daughter, ages 3 years and 18 months. Gano has settled into "a one-room dive that I share with my brother" in New York's East Village, but the two family men still live in Milwaukee.

Time at home these days is rare. After concert tours through Europe, Australia, New Zealand and the U.S. this year, the Femmes have taken a three-month hiatus, and Gano is now working temporarily with a gospel punk band. Ritchie, meanwhile, is considering a solo album, and De Lorenzo is producing a new LP for an all-girl Milwaukee group.

The short summer break may give them time to adjust to their growing fame. Ritchie recently boarded a Milwaukee bus only to confront three teenage fans bursting into an a cappella concert of Femmes hits. "Now I'm hesitant to ride on the bus here," he says. It's a small problem, most likely; local buses probably aren't going to be the Femmes' mode of transport much longer.