WE PUBLISH on the opposite page today an authentic man-bites-dog item, a penetrating and reasoned critique of the United Nations system as it actually operates by someone who is a creature and servant of the system, its secretary general, Javier Perez de Cuellar. He has been up there on the 38th floor for less than a year, but already he sees and, more importantly, expresses publicly the disappointments that have been felt by a covey of other, outside critics. He understands precisely why the United Nations has fallen into disrespect and disuse, and he is in effect putting his job on the line in order to try to do something about it.

Many people might share Mr. Perez de Cuellar's conviction that the international community is "perilously near to a new international anarchy." He is that rare international person who is not so jaded by worldly cynicism or enfeebled by institutional self-pity as to figure that not much can be done. To improve the United Nations, the secretary general recommends a series of changes in procedure and attitude. None of these changes would require a transformation in the nature of man. They would really do little more than infringe to a degree on the concept of sovereignty that lets individual nations preen and pontificate at the expense of the common good.

Often the "critics" of the United Nations are juxtaposed to its "supporters." But Mr. Perez de Cuellar fills, handsomely, both bills. Nothing he has said will please everybody: the Reagan administration, for instance, having just launched its own Mideast plan, may be slow to hail his call for even a less "partisan" United Nations to get out front in that area. A grand Security Council summit to discuss his and like proposals would be some affair. His broad purpose, however, cannot fail to stir those who uphold the Charter's commitment to world peace, and to unmask those who merely pretend.