One by one, they drifted on to the stage, most of them in sweaters or shirtsleeves. They settled into their seats, and the buzzing audience quieted as Symphony Hall was filled with the familiar warm sounds of instruments tuning. A violist in a green sweater, blue trousers, and loafers shuffled past the podium, east a disdainful glance at the audience and sat down.

"This is a rehearsal," announced the assistant manager, "and at rehearsals there are no interruptions, no applause. You must imagine yourselves behind a glass wall or curtain. Of course, I do not see how you can restrain yourselves for Mr. Munch and Mr. Menuhin."

Mr. Munch entered, grinning at the unrestrained audience. He turned to his orchestra, glanced at the microphone which hung over the center like a patient bee, and led the brasses through Gabrieli. For Schoenberg's "Kammersymphonie" he abandoned his high stool and put on his glasses. He bounced around the front of the podium, swinging his arms from side to side for the sharp, biting chords, then shook his head at a chord too harsh even for Schoenberg.

"Theurteen," he said. "Back to theurteen."

After a few minutes, Munch waved his hand.

"Is all right now," he said. "Schumann."

There was a rustle as the orchestra buried its Schoenberg under the Spring Symphony scores. About midway through the first theme statement, Munch came down from his cager tiptoe level.

"One spot. Just this spot--ta-ta-TUM." The orchestra imitated the syllables. "Once more, together now."

The results were satisfactory; a beatifie grin spread across his face. A shock of iron-gray hair dropped lower and lower over his forehead, and then the grin faded.

"Shh," he told the strings. "Too much fortissimo. Too much . . .B FLAT" he roared suddenly at the brasses, then returned the admonishing index finger to the strings. He stepped down from the podium, advanced into the orchestra with his hands spread in front of his chest. "She. Peaceful." As he stepped back the smile returned. "Excellent now," he said.

The second movement was warm and lyrical. Munch looked tenderly at his violins, and learned over to the first row.

"Sing," he said softly. "Sing." They sang.

In the scherzo there were a few false starts, and each time Munch followed the same pattern: a pause, a violent gesture, and a grunt--then the theme.

"The first beat only accented, gentlemen, so, BAM, bam bam bam." The crepe-soled palomino sport shoes thudded the beat, and the orchestra compliead.

"Good," he said, and motioned toward the door. "Mr. Menuhin."

Mr. Menuhin waved happily as he strode in, his blue sport shirt flapping outside his trousers.

Munch tucked his stool under himself and nodded the beginning of the Mozart concerto. Mozart was fine, and his eyebrows touched the hanging edges of his dishevelled hair as he grinned at Menuhin.

"Sing," he invited. "Go ahead. Sing." The violin flashed.

At the end of the concerto, the orchestra murmured its bravos, and Munch and Menuhin strode off, Menuhin waving cheerfully. The violist in the green sweater explored the floor around his chair with his foot, slipped his loafers back on, and shuffled off, looking over his shoulder as he went.