Brahmsday

''Exit in case of Brahms.'' Such a doorway was suggested when Boston's Symphony Hall was being built around 1900. People had been known to walk out when Brahms was played.

The music of Germany's Johannes Brahms has become so internationally admired that we hesitate to note our own town has special reason to honor the man whose music it once scorned. But, tomorrow being the 150th anniversary of his birth, we press on regardless.

The Boston Symphony Orchestra must be the only one whose first conductor, Georg Henschel, barnstormed Europe as a singer - with Brahms as his piano accompanist. (Even when he was conducting the BSO Henschel sometimes handed his baton to the concertmaster long enough to sing a piece or two. But that is another story.) Henschel also asked and received advice from Brahms on how to arrange the seating of the new orchestra.

Naturally Henschel, who had taken composition lessons from Brahms, assumed a responsibility for making local audiences familiar with his friend's music. One ungrateful critic wrote:

''We are told by an eminent musician of the Orchestra that thirty years will make a wondrous change in our views concerning Brahms's idiosyncrasies. Let us not run so unwelcome a risk.''

An early BSO program editor looked back on days when Schumann and Wagner also had a long struggle for recognition. Liszt and Berlioz ''frightened almost all listeners'' at first. ''And when Brahms came, he seemed the hardest nut to crack of all.''

Can we believe it now, when Brahms can still sound marvelously fresh as well as beautiful - but pours comfortably over us instead of sending people to the exits? Is there hope for a Brahms among composers that drive some listeners up the wall today? Will the world ever have another symphony orchestra with a singing conductor?