In a midtown parking garage, while the night ladies listen, a four-man Latino band practices its protest songs on cracked guitars.

Crammed into the ticket booth, Grupo Izalco quavers through the harmonies of a "mojado" lament -- a "wetback" ballad -- hissing the maracas part and ducking their heads to the midnight customers of the garage.

"Aiyy, muchachos!" groans David Marcus after "Guantanamera" founders. Then he begins rapping out a fresh rhythm. "We're still working this one out."

In a city full of corner musicians, these are sidewalk serenaders with a mission. Izalco, named after a volcano in El Salvador where as many as 30,000 Indians are said to have been massacred by government soldiers in 1932, wears its social protest passion on its business card.

The members of the group, three transplanted Salvadorans and Marcus, a native of California raised in Mexico, have to moonlight as musicians, rehearsing around Enrique Diaz's night hours at the garage ("It has great acoustics") and saving money for new instruments. Although most of the music is arranged for guitars, group members also play violin, trombone, mandolin, drums, accordion and panpipes.

The band's repertoire includes "popular folk and protest music" from Puerto Rico, Honduras, Nicaragua, Costa Rica, Guatemala, Mexico and Cuba. It rambles from a tribute to the poor coffee pickers of El Salavador, who work only three months a year, to a scathing Argentine sketch of "Los Americanos."

"A lot of what's called 'nueva cancion' -- new music -- has been written in the last 20 or 30 years," said Marcus. "It's social issue stuff. It sort of corresponds to the kind of music being written here in the late '50s."

On the other hand, Izalco has been known to meander into the middle of the road for such sentimentalities as "Take Me Home, Country Road" (Victor Gonzales' favorite) and Diaz's romantic solos, "On the Street Where You Live" and "I Left My Heart in San Francisco."

"Anything from profoundly schmaltzy love songs to rousing popular chants," Marcus shrugged. "We cover the waterfront."

Marcus, Diaz, Gonzales and Jaime Caballero met through the Cafe Casa del Pueblo, a weekend coffeehouse that operates out of Calvary United Methodist Church at 1459 Columbia Rd. NW. They played together in various combinations and then formally joined forces last summer.

"The first time was at the Hispanic festival in Adams-Morgan" last July, said Marcus, who is the educational and cultural coordinator of the Casa del Pueblo Ministries. "We put out a hat and we couldn't believe how much money we made."

It was not a reliable financial omen: Most of the group's performances have been at Hispanic cultural or educational events, fund raisers and marches, none of which adds much to the instrument fund.

"We've played every Unitarian church in the metropolitan area," Marcus said with a wry grin. "That's an exaggeration, but you get the idea."

All are experienced musicians. Diaz, the senior member, says he was a member of the Salvadoran national chorus and a well-known serenader. Caballero, whose high school sponsored student festivals that were "all protest music," played in a dance band as a hobby.

Gonzales was part of a quintet that was featured on Salvadoran educational television in the late '60s, he says, singing English-language lessons for junior high school students. Marcus is a relative newcomer to folk music who used to play jazz piano.

Last weekend, Izalco headlined a Boston rally for a Central American refugee organization that drew 1,500 people, their largest audience to date. The band has been invited to perform this summer at the Washington Folklore Society's festival in Glen Echo and at the Folklife Festival on the Mall.