Three and a half decades ago the parents of America were brought up short by the depiction, first in a book by Evan Hunter and then in a film by Richard Brooks, of the public school system as "The Blackboard Jungle." The prevailing assumption that school was one place where a child could be insulated from the unpleasantness of the world outside was turned on its head by this portrait of teachers and fellow students terrorized by teen-aged thugs and schoolyard bullies; "blackboard jungle" quickly became as much a catch phrase of the 1950s as "power elite" and "hidden persuaders" and "man in the gray flannel suit."That, to put it mildly, was yesterday. If you've run across "The Blackboard Jungle" on the late-late movie recently, you're well aware that it now seems almost comically dated and naive. Not merely are its students dressed in the garb of what seems another century - bobby socks, pegged pants, crew cuts - but its language and physical action are hopelessly tame by today's standards. Across the nation there must be thousands of high school principals who would gladly - no, gleefully - settle for troubles so trivial as those with which the administrators and teachers of that movie were afflicted.

Consider by way of example the high school principals of Baltimore. Under the leadership of its new mayor, Kurt Schmoke, and superintendent of schools, Richard Hunter, that city is strongly committed to improving the quality of education in a system that has been visited with every variety of plague now common in the urban schools, but the two and the principals who work for them hardly have a moment to concentrate on questions of curriculum or educational policy. Instead they are fighting a desperate rearguard action against a wave of schoolyard violence that has students and parents apprehensive at best and terrified at worst.

In the past three weeks there have been four handgun shootings and two rapes at or near Baltimore schools. None of the wounded students was killed - by merciful contrast with the case of the Baltimore schoolboy who was shot to death a few years ago when he refused to hand over his Georgetown basketball jacket to a few young gangsters - and not all of the suspects have been identified, but in the minds of Baltimore parents these details are of less urgency than the general fear that their children simply are not safe within the grounds of the schools they attend.

Thus it is that Richard Hunter and his assistants are under terrific pressure to put safety first and education second.

All of which is to say that the schools in Baltimore are now in effect the prisoners of a handful of children. The control of this violence is now the principal responsibility of the school system's administrators and teachers; it is no exaggeration to say that it has become the chief occupation of their working days.

So who can blame one of them for speaking bitterly about this latest turn in his professional life? He said it would be nice if parents began to assume a bit of the burden of teaching and disciplining their own children. The schools already are expected to teach children everything from sexuality to driving, and now we insist that they take on the functions of the police department as well. Why, this gentleman asked with admirable restraint, can't parents themselves take on some of these disagreeable but necessary chores?

It is a good question, but one certain not to receive a satisfactory answer. Not merely have too many parents sloughed off too much of their traditional roles as instructors and nurturers, but inevitably what goes on in the schools reflects the behavior of society as a whole. In a large American city in the late years of the 20th century, this means an acclimatization to violence.

It may be a truism to say that before we change the schools we must change society, but truisms usually get that way because they happen to be true. We cannot expect young people to honor standards and modes of behavior that we ourselves repudiate.