There is a new menace in the concert hall these days. The young child. Or perhaps children. Or parents with small children. Let me illustrate with a story whose truths are more powerful than anything it might have occurred to me to invent.

On a Sunday eveing at the National Gallery a young singer was moving through one of the most serious songs on the program. As the softest moments in the song approached, suddenly, with something of the effect of someone scratching a large blackboard with a long fingernail, the sound of an infant filled the area surrounding the singer, the pianist and the audience. (Those who were listening on the radio thought for a moment that someone had decided to squeeze a noisy rubber doll.)

It was not at all clear whether the cries were of joy or pain -- they are so close, you remember. Since they quickly subsided, the listeners returned their attention to the singer and the song. But the young Sutherland -- or was it a Pavarotti? -- was far from finished. Again, and yet again, in the next minutes, and during other songs, the gleeful -- or miserable? -- gurgles shot through the hall. At last, the guard, who had been waiting, hoping that the interruption would end without his intervention, went over to the parents and asked them to take the kid out.

Well ! Put yourself in the place of any of several people: the parents, the music director of the Gallery, the parents of the singer. What would you have done?

At the close of the recital, Richard Bales, who has presided over National Gallery concerts for lo these several decades, went over to the parents. In his most gallant manner, and there is no more polite gentleman in the City of Washington, Bales said something like, "We love to have the children come to the concerts -- but in the future, could you leave the youngest ones at home?"

Sounds reasonable, doesn't it? Apparently not. While the mother was tending to the noisy youngster, the father shot back an indignant, "Well! If that's the way you feel about children here at the Gallery, I will take the matter up with my congressman. After all, this is a public gallery!"

Let me hasten to assure you that the minor embroilment ended with mutual assurances of friendship and admiration. But the singer's interrupted song remained unrepaired. As the children and their mother were leaving, they happened to meet the singer's mother. "Ah, you are the mother of the singer," said the mother of the child. "My son was having such a good time he joined in with the singing!"

"That's always always so nice for the singer," replied the mother of the singer.

Now I should make it clear that both Bales and I are parents and fond of children. But is this some new assertiveness on the part of parents to bring the little kiddies to concerts before they are old enough to understand that while the music is going on, no one makes noises?

What Bales obviously overlooked was that the parents of four children are not going to hire a babysitter for the one who may be too young to take to concerts. Shich means that either the youngest one will keep on turning up and singing along, or maybe mom and pop could take turns going to concerts with the older kids.

Lest you think that the National Gallery incident was an isolated case, then know that the very same thing happened a few weeks later at renwick Gallery on a Sunday afternoon when two young American artists were presenting one of the finest song recitals heard here in some seasons.

Same scenario: At the quietest moment in a song by Schumann, restless children whose parents ought to have known they would not want to sit and listen to Schubert, Schumann, Strauss and Wolf, began to move around the room, talking and making other noises. Unlike the National Gallery guard, however, neither of the two guards at the back of the Renwick's Music Room moved a muscle to stop the racket. (Since they had been talking much of the time themselves, it was hardly to be expected that they would.)

Another week or two, and the scene is the Phillips Collection at 5 p.m. on a Sunday. A young couple is there with infant-in-arms. Before the music began, Charles Crowder, director of the Phillips concerts, asked the parents if they thought their child would be happy and quiet when the music started. Oh yes, they were sure. Guess what?

The pianist was hardly halfway through the first of two sonatas by Soler before a lusty "Nyaaaaa..." was ringing through the room. An air check of the concert would show that it carried easily to the microphone some distance away, to say nothing of the entire audience. In some embarrassment at having been shown up so speedily by their offspring, the parents beat a retreat at the first chance. Perhaps Crowder has the right idea when he says, "I am thinking of putting up a sign saying, 'No children under 12, please.'"

Do not think for a moment that payment of admission prevents these infantile invasions. I have the word of a loyal National Symphony subscriber for the following:

A family arrived for a subscription concert, bringing children, ages 3 through 7, with them. As the music proceeded from loud to soft -- why is it always in the soft passages, like coughing? -- a strange rustling sound began to make its way into the air surrounding other subscribers. Persistently it moved, crackling, popping, just loud enough so that those for some distance around were much more aware of the sibilances than they were able to be of the music.

The little innocents were unwrapping candy bars. They were doing it ever so slowly so as not to make a sound! No quick rip and bite for them. Slowly, slowly, now, and without a sound. Hmpf. That's what they thought.

When, at last, the indignation got to the point where open protests were made to the kiddies' mommy, she came back with a combination of hurt and indignation: "Take away their candy!? But I gave them the candy to keep them quiet!"

I have discussed this problem with various friends, among whom are authorities on child behavior. I need only name Miss Manners. We are in complete agreement that children can be taken to concerts. Ours were. Hers were. Thousands of others were. But only when they were old enough -- it can happen at 3 or at 13 -- to realize that at a concert the music is the overriding concern, and that therefore, while the music is going on, whether you are 3 or 63, you keep still . (Strange how closely children tend to imitate their parents.)