When U.N. Ambassador Andrew Young Jr. did it, is cost him his job, shattered black-Jewish relations here sent diplomatic shockwaves through much of the world.

When U.N. Ambassador Jeane Kirkpatrick did it, nobody even found it necessary to offer an official explanation.

The point is not so much the differential treatment of two ambassadors apparently guilty of the same offense -- violating official U.S. policy by talking to diplomatic pariahs -- but the differential respect for the policy itself.

Young, perhaps with the tacit approval or President Carter, violated the Kissinger-era policy against "substantive contact" with the Palestine Liberation Organization.

Kirkpatrick, with the apparent blessing of President Reagan, violated the policy against dealing with members of the South African military. The very presence of the high-ranking South African military-intelligence officer in the United States was a violation of policy dating back to 1967.

Indeed, the limitationon official U.S. contacts with South African military officials was initiated during the Kennedy administration as an adjunct to the U.N. voluntary arms embargo against South Africa.

Could it be that the visit of the South African military officials, including the chief of military intelligence, is part of the unquestioned movement of the Reagan administration toward warmer relations with the only officially racist regime in the world?

State Department officials say no.

Did the South Africans lie about the nature of their jobs, pretending to be only "foreign affairs officials"?

The South Africans say no.

The episode apparently began in late February when officials of the private American Security Council notified the U.S. State Department of their intention to invite Lt. Gen. Van Der Westerhuizen and two other high-ranking military officials to Washington for an "internal briefing and seminar on the situation in South Africa." Since the officers would not apply for visas without assurances that they would be granted, would State Please say whether the visit would be approved?

State told the ASC officials that the visas would not be granted.

On March 7, State received another letter asking how the ASC should proceed without risking the embarrassment of a visa denial.

But meanwhile, on March 2 and 3, the U.S. Embassy in Pretoria had already received visa applications from the prospective visitors, who describe themselves as "foreign affairs officials." The visa applications were approved in Pretoria.

Donald B. Sole, South Africa's ambassador to Washington, said there was no attempt to mislead the American authorities.

"It is correct," he told me, "that the South African Department of Foreign Affairs did not, in a formal note to the U.S. Embassy requesting the visas, disclose the nature of the duties performed by the gentlemen in question, but surely it is accepted that, when visas are sought for persons employed in intelligence, this fact is not spelled out in the accompanying formal note."

The clear implication of Sole's explanation is that the Americans knew what they were doing.

But did they? Embassy officials in Pretoria said the visas were issued routinely and that the names -- common in South Africa -- triggered no suspicion.

But surely Kirkpatrick knew who Van Der Westerhuizen was when she met with him in New York on March 15. State officials, who by then had learned the nature of the visitors' official duties, had been told by Ambassador Sole that they would be leaving the night of March 14. (State denies the UPI report that the meeting with Kirkpatrick was arranged "at the request of the State Department.")

The more troublesome questions, however, have less to do with sloppy visa work than with the pro-South Africa tilt of the Reagan administration.

The firestorm of protest that followed Andy Young's meeting with a PLO representative had less to do with clear danger to U.S. international interests than with the outrage of American Jews. That outrage clearly mattered to the Carter administration.

Similar outrage on the part of Americans, black and white, and on the part of virtually all of black Africa, seems not to matter to the Reagan administration.

Quite apart from whether Reagan has any duty to be sympathetic to the concerns of black Americans, who, after all, voted overshelmingly for his opponent, the shift in official American attitudes toward Africa seems certain to create massive difficulties for the Reagan administration -- and for America -- with hardly any compensating advantage.

The major problem with the new Reagan policy is not that it lacks sensitivity but that it lacks sense. It is certain to cost more than it's worth -- in mineral resources, in domestic stability and in international relations, particularly with regard to black Africa.

The unanswered question is: Why is he doing it?