Composer George Crumb, who assigns singers extraordinary jobs to do in addition to singing, was in town recently to talk about his vocal music. He spoke to a session of the National Association of Teachers convention; and the Theater Chamber Players included Crumb's "Night of the Four Moons" on the program it offered the teachers at the University of Maryland.

In "Night of the Four Moons," soprano Phyllis Bryn-Julson, who led a discussion of the work, not only sang; she also hummed, played finger castanets and tiny finger cymbals, a small xylophone and a minigong. She also whistled.

At times her voice quietly intoned a lullaby, "Nino, nino." The next moment, she took off in a high-pitched frenzy of excited, scolding sounds. Her accompaniment was played altoflute, cello (amplified), banjo and an assortment of percussion instruments that included bongo drums, a temple gong, Kabuki wood blocks and a miniscule thumb piano.

Toward the end of the piece, Bryn-Julson led all the other performers off-stage except the cellist. As each one left, he gave a single tap on a small gong placed by the exit. Then, with magical effect, the voice mingled with flute and thumb piano in a final, distant serenade, while the lights in the hall gradually went completely dark and no sound remained except the cello, wavering pianissmo between two high half-notes.

These extra-musical elements have been present in much of Crumb's music for the purpose of adding a powerful sense of the dramatic to his notes. Often they have stemmed from implications in the texts of Garcia Lorca, who has been, until lately, the principal literary stimulus to Crumb's composition. In all of his music, Crumb has not hestitated to give specific directions for theatrical devices that heighten the impact of the music.

Thus in "Echoes of Time and the River," which won Crumb a Pulitzer Prize 10 years ago, the trombonists of the orchestra not only marched around the playing area. They also whisper through their instruments while lined up in front of the ensemble. (In this case they whisper the words, "Montani sunt semper liberi," which is the state motto of Crumb's birthplace, West Virginia. It means "Mountaineers are always free.") In the same way in "Night of the Four Moons," both the flutist and percussionist add whispering to their playing duties.

Whether in his big and famous pieces for prepared piano, called "Makrokosmos," which now number three volumes, and which are inspired by the ancient and philosophical meanings of the signs of the zodiac, or in his mysterious work for eletric string quartet called "Black Angels," Crumb's music is always centered around sonorities and textures.

"I am through with my Lorca phase," Crumb said at the University of Maryland. "I have not written anything more on him for sometime." His largest orchestal work, "Star Child," which had a successful New York premiere last season, uses medieval texts. "It is a very big piece," he said. "While it lasts only about 35 minutes, it calls for large orchestra plus extra instruments, children's choir and a mezzo soloist.And I have found that to ask for such resources tends to limit the number of performances."

Since the composer was present during the rehearsal of his "Four Moons," both the performers and the singing teachers had questions for him. "About the tempo of the Spanish dance episode," Dina Koston, the Chamber Players' founder and artistic advisor, began. "We have done this work before and have had strong disagreements about the speed at which that part should go. It is marked 90, but Leon that is likes it much slower, for a more sensuous effect."

"Yes, I noticed that you took it slower than it is marked," Crumb replied. "Try it again at the faster tempo . . . 90," he continued with the quiet modesty that is one of his trademarks, "is really the speed I had in mind for it."

The musicians took up the passage, this time with Fleisher conducting, which he had not done previously. Even so, he did not get it quite up to the tempo marked. When Bryn-Julson turned to the audience and asked for a show of hands, the large majority preferred the faster pace.

Then someone in the audience objected to the loudness of the wood blocks, which in the extremely live acoustics of Tawes Recital Hall came acros like rifle shots.

"This is a very resonant hall," Crumb began, in answering the complaint. "I heard things today that I have never heard Before becaue of the unusually live sound. But those are Kabuki blocks; they are used in the theater. And they are meant to be loud." To these remarks by the composer, the percussion player added." "And besides, they are marked 'sfffz,' which indicates a very violent, sudden kind of loudness."

George Crumb knows exactly what he wants. And, blessed with a phenomenal aural imagination, knows precisely what to ask for to achieve it.