It was like a real concert. Pierre Monteux walked slowly to the podium, acknowledged the applause, and began conducting the Boston Symphony Orchestra in a program of Wagner and Debussy. Only the informality of the orchestra members, the smallness of the crowd, and the infrequent interruptions by Monteux showed that this was just a rehearsal.

One can easily understand why Monteux has achieved such a high position among the world's conductors. The elephantine Frenchman handled the orchestra as if he owned it. He led it safely through the rhythmic complexities of Debussy, and went on to revitalize a bunch of Wagnerian warhorses that have been all but killed by dozens of inept performances. The response to Monteux's steady, relaxed beat was nearly perfect, and the obvious rapport between conductor and orchestra resulted in quick run--throughs of most of the music.

Thursday night's open rehearsal was the first of five to be given this year chiefly for the benefit of students who can't attend the real thing. The next one, on December 13, will be conducted by Ernest Ansermet, substituting for the ailing Charles Munch. In many ways, a rehearsal is even more enjoyable than a concert. The informality contrasts favorably with the machine-like view one usually gets of an orchestra. Watching them chatting among themselves and pencil-marking their scores, one can appreciate them as human beings. Unfortunately, the audience could not hear most of Monteux's remarks. Perhaps next time a microphone will be placed somewhere near the podium.

The peak of informality was reached at 9:59, when all one hundred musicians, in the midst of a big crescendo, suddenly rose, closed their music, and left the stage just in time to beat the Musicians' Union's deadline.