"I'm sending out a page of definiations of foreign language terms," conductor Barry Hemphill informs the 90-member Arlington Metropolitan Chorus. Then, teasing, he adds, "There will be three full pages of Brooklynese."

The chorus won't need them. Now beginning their fourth season with Hemphill, the singers have learned to interpret his elaborate body language, and they respond like a school of fish to his evey articulate wiggle.

During a recent rehearsal for their Christmas music performance, scheduled for Dec. 6 at Kenmore Intermediate School in Arlington, Hemphill gave a vivid demonstration of Brooklyn Body Language.

Looking for all the world like a ballet master to Zorba the Greek, he starts in a perfect first position -- arms at shoulder height, head angled upward and eyes closed. He points his fingers up (which means "hold the note"), wiggles them ("more vibrato"), stomps his foot ("keep to the rhythm"), claps once ("stop!"), and tells them, "Chocolate pudding (this isn't working)."

He admonishes the baritones not to "sneak in like that. I'd rather you be big and bad and bold and wrong than sneak in." Starting the group again with "and," he pushes them through an arduous section by leaning over and giving them Afican folk-dance claps. Then, with a smile, he stops, collapses on the stage steps and gives out a long wolf whistle. "That was veddy, veddy, veddy, veddy good," he says, using an accent not his own.

The accent is borrowed from Hugh Ross, choral man to Arturo Toscanini and Hemphill's boss after college. Hemphill left the Manhattan School of Music ("I'm a Brooklyn boy, all the way!") and went through "a hell of an audition" with Ross, emerging with a job with his madrigal group. "Then, after only a year, he made me a conductor," says Hemphill with a grin. "It's not supposed to happen that fast."

Ross was a major influence on Hemphill, but less so than Hemphill's father. "You might say I come by my music naturally," he says. "My dad played first trumpet with Duke Ellington. I had babysitters like the Mills Brothers," he reminisces, "and Billy Holliday. She was a nice woman who fed me fried chicken and held my hand while my dad played."

His father started Hemphill on music lessons at the age of 4. "But I had to drop them at 6, when my front teeth fell out -- truth. You can't play a horn with no teeth."

His father stopped playing at about the same time, for health reasons, and took a job as a night watchman for the New York City Housing Authority -- "even though he's a college graduate. My mother was doing graduate work at the time in psychology, and they worked out a deal where one of them would always be home with my sister and I. We got a lot of love."

He also got a lot of lessons, including folk dancing and ballet -- the latter to improve his basketball game. "When you're my height, you've got to make up for it with fancy footwork," says the 5-foot-10 conductor. "One day I walked by a room where a ballet class was going on, saw the footwork they used, and decided to try it. Besides, it was a roomful of 30 women," he says slyly, "and me."

But brass continued to be his major love unitl halfway through college when he became interested in choral music. "I didn't know anything about it," he says, "and decided, like the old Indian adage, to walk a mile in their moccasins."

On a European tour with Ross, Hemphill met the famous choir director Norman Luboff. Waiting in the mail when he came home were two offers: a contract from Luboff and greetings from Uncle Sam. It was 1968.

Uncle Sam's leter took precedence and Hemphill was drafted into the Army. "I heard about the Army chorus and came here to join in 1969," he says. He has been in Northern Virginia ever since.

Like many musicians in the military, Hemphill uses his free time to do civilian work, including a number of conducting jobs for the Arlington Performing Arts Department. Through them, he heard that the Arlington Chorus founder and conductor, Vera Tilson, was resigning, and he lined up with the others to audition for the job.

"It came down to eight people," says Dan Boo, then president of the chorus. "They were all good, but Barry was the best. He looked as if he was ready to deal with a less-then-perfect group and improve discipline, which can be a problem in a volunteer group like ours."

Hemphill admits the group was "sloppy" when he began, but insists he was left with a "good nucleus of people to build on, which is the hardest problem. Washington," he says, "is becoming known as a choral town; there are at least a dozen community groups in the Metro area, not to mention college groups. And we will compete for talent.

"But I'm drawing a high quality of people now to the auditions," he says, "and the group has grown musically by leaps and bounds. It's the best single group in the suburbs," he boasts.

The admiration is mutual. Among its suburban mix of senior citizens, bearded civil servants, career women and housewives, you will not hear a bad word about Hemphill. "He's a wonderful musician," says Virginia Vickers, who has sung with the chorus for 12 years, "and very good with people. He bawls us out when we need it, but he pats us on the back, too."

Ezra Glazer, who has been with the chorus from its beginning, says, "I've seen choruses where the conductor stops every few measures and lectures on the music. Barry doesn't stop -- he doesn't have to."

The energetic conductor is poised again in first position, arms raised. And with a Brooklynese flick of his fingers, the music begins once more.

This time, it's not chocolate pudding.