WELL, YOU MAY SAY, what's so wrong with American delegate Brady Tyson's apologizing at Geneva for U.S. involvement in subverting Chile in 1973? Didn't Jimmy Carter himself campaign against that Nixon policy? Doesn't now-President Carter wish this country to set an example in moral concern? Why did the State Department and then the President slap him down?

What's wrong is that the Tyson apology represents the latest manifestation of what might be named the Andy Young problem, in honor of the man who appointed ambassador to the United Nations. Drawing on his close association with the President and pronouncing himself a "point man," he has offered one public judgment after another that turns out to have been neither cleared in advance nor approved afterward by the administration. Mr. Tyson is in effect Andy Young's Andy Young: after Mr. Tyson spoke in Geneva the ambassador said that before commenting he wished to see the full text, which is precisely the sort of thing that Secretary of State Vance and other officials have regularly found themselves forced to say after some of Mr. Young's pronouncements. So now, perhaps, Mr. Young knows how it feels.

No one denies Mr. Young, or Mr. Tyson, the right as a public official to lobby in channels for his personal views. But foreign governments and the American people understandably expect that public statements made by officials in appropriate forums represent the policy of the U.S. government. The President has a right to expect that officials speaking in his name express his administration's views. There is a necessary presumption of good order. Foreign governments are not interested in the personal views of American officials; they want to know what is the official policy.To toss off personal opinions - or to play "point man" - and then to be repudiated is to lose a certain part of one's claim on another govenment's or the public's attention: to lose effectiveness.

In Mr. Tyson's case, the central point is not that he thought he was expressing the President's viewpoint but that he was taking upon himself an extremely rare and sensitive decision - to formally apologize, for a country as well as for a government, for the controversial policy of a past administration. Surely that decision is weighty enough to deserve being left to the considered opinion of the President and his top advisers. A President who did not assert his own authority in such a matter would be inviting constant disorder and embarrassment.

Given his ties with the President, Ambassador Young's case is special. Or is it? Is he really immune from the departmental or presidential discipline that, however personally constricting, is finally what can give true force to his ideas? Does he want that sort of immunity? We applauded Mr. Young's appointment, believing that he had a solid contribution to make to the shaping of American foreign policy. We would no want to see his influence wane before he had barely begun to wield it.