When Julius Hemphill and the D.C. Jazz Workshop Orchestra appear Sunday night at Gallery Place during the Add Arts '85 festival, they'll perform an overture to a work in progress called "Long Tongues," a proposed three-act saxophone opera scheduled for a Washington premiere in 1987.

The opera grew out of a collaboration begun several years ago between Hemphill, best known as a member of the widely acclaimed World Saxophone Quartet, and District Curators Inc., which is producing the work. In 1979, the same pairing produced a jazz/theater piece called "Ralph Ellison's Long Tongue," which was presented at both the Corcoran Gallery in Washington and the Kitchen in New York.

Though some elements of that production will be retained, including the idea of the jazz world seen through the eyes of a nightclub janitor, the opera is a far more ambitious work. As outlined in a recent National Endowment for the Arts grant application, "The Long Tongues" will be "an unconventional operatic treatment of the history of modern jazz and the concurrent social and cultural changes in the U.S. -- more specifically, in Washington, D.C. -- after World War II."

As proposed, the opera will trace the history of jazz from be-bop to free form and interpret it "through visual information, movement, and saxophone music as the spoken word." It will be set in Washington, with a nightclub janitor (who serves as the narrator) employed at the Bohemian Caverns, a hotbed of jazz in the '50s and the '60s.

The dramatic treatment will be written by Hemphill and Washington journalist W.A. Brower. Poet Greg Tate will write the part of the narrator, and Hemphill says his colleagues in the World Jazz Quartet will be involved in the production as well.

For now, though, Hemphill is merely getting his feet wet. Earlier this week he began practicing with the Workshop Orchestra for the first time, preparing for Sunday's concert.

"I plan to include some songs that may end up being a part of 'Long Tongues' and some that may not," says Hemphill. "We'll be covering a lot of music, not just pieces related to the opera . . . first things first. I'm told we're going to have a large audience this weekend and we want to put together the best kind of program we can . . . Some of the pieces I've performed before with various ensembles, including the World Saxophone Quartet.

As for the opera, Hemphill says the major challenge will be "authenticity: making it plausible . . . there's more to this than just chronology."

Hemphill seems an ideal candidate to undertake a project like "Long Tongues," and not just because he's a highly regarded jazz saxophonist and composer. Over the past 15 years he has been involved in a variety of jazz and theatrical productions. "I've been mixing media for a long time," he said. "I've made a film and videos and even been an actor at times."

Hemphill says it was sports, not music, that mostly occupied his mind while growing up in Fort Worth, even though the "community was rich with musicians. My peers were into sports so everything was football back then," he said.

Even so, Hemphill played the clarinet in the high school marching band, discovering along the way that he could transfer many of the same clarinet fingerings to the saxophone.

"That was one of the biggest thrills of my life, finding out I could play the sax," he said. "I was listening to all kinds of music back then. There was this jukebox across the street from where I lived and they'd play tunes by Louis Jordan and follow it with something by Sister Rosetta Thorpe, all these incongruous sounds . . . eventually, I got to see some of the people I'd been hearing about -- Bud Powell, Lester Young, Nat Cole, Illinois Jacquet."

Hemphill says he went off to college with thoughts of becoming a doctor only to discover that he was better equipped to pursue music. He played in numerous southwestern blues bands, studied harmony under David Baker at Lincoln College and, after a hitch in the Army, moved to St. Louis where he organized the Black Artists Group in 1968.

"We were a collective of poets, dancers, actors and musicians, people interested in all the major areas of the arts," Hemphill says of the BAG. "Those were extraordinary times. I had never had the opportunity to participate in such a mix of talents. And neither had anyone else. We just kept knocking each other out, pooling our talents to put on a concert or a drama or whatever."

To Hemphill, the "most radical" thing to emerge from the turbulent jazz scene in the late '60s wasn't the music, but rather the approach to presenting music. "The idea that you could bypass the clubs and just get a room or a hall or some place and present the music the way you wanted to -- that was really different and exciting," he says. "All of a sudden we had these options and opportunities that weren't there before. I started looking at jazz more and more as a theatrical presentation . . . here was a different mode of expression."

It's funny, he says, that critics often point to how daring the World Saxophone Quartet is for operating autonomously, without a rhythm section. "I've been part of so many different kinds of theatrical presentations, combining jazz with painting, dance, drama, that working without a rhythm section seemed like nothing to me. We had already done that years ago."