The South African government intervened at the last moment to stop a visit by Dennis Norman, Zimbabwe's only white Cabinet minister, and two other prominent whites who were to address a group of white Zimbabwean students at the University of Cape Town, saying their visit would be "inappropriate" at this time.

The decision, apparently taken at a Cabinet meeting earlier this week, is another manifestation of Pretoria's displeasure at public criticism of South Africa and its racial policies by Zimbabwean officials and is expected to strain relations further.

"What it really says is that a Cabinet minister, even if he is white, is not welcome in this country," said John Barrett, director of the South African Institute of International Affairs.

But Barrett pointed out that Zimbabwe also is discouraging visits here by officials. The head of the state-run radio and television, Willie Musarurwa, who was to attend an institute conference later this month, canceled his visit two weeks ago due to pressure from his government, Barrett said.

By a number of actions over the past few months, South Africa has made clear that it is not prepared to go along with Zimbabwe's preference for a dual-level relationship -- which would require Pretoria to tolerate Zimbabwe's critical rhetoric and at the same time maintain cordial economic relations in private. South Africa has pressed for normal diplomatic ties.

Some observers have suggested that the fact that Norman, Zimbabwe's minister of agriculture, was only to see students, and not officials here, contributed to the decision to bar him.

South Africa has been angered by accusations from Zimbabwean officials, including Prime Minister Robert Mugabe, that South African agents were responsible for the assassination of anti-Pretoria activist Joseph Gqabi in Salisbury July 31.

"With all the things coming out of Mugabe's government it was not clear to us what he Norman was coming here to say to the students," an official said. But it is unlikely Norman was about to say anything inflammatory. Rather, the gist of his speech, like the others, was likely to have been to encourage graduates to come home and contribute their skills to Zimbabwe's economy.

Norman, businessman Brian Grubb and politician Andre Holland were all telephoned Tuesday by the South African trade mission in Salisbury and advised their visit the next day would be "inappropriate," Grubb said.

Grubb said he found the decision "extraordinary. I was just going to talk to my fellow countrymen about the business climate as I see it. I don't see what is wrong with that."

The men had been invited by the Zimbabwe Society, which represents about 900 Zimbabwe-born students at the University of Cape Town. Society president David Coltart said he had no comment on the decision but said most of the students, of whom about 600 still consider Zimbabwe home, were "absolutely dejected" because they had looked forward to hearing "some of the good news" about Zimbabwe. Much of what appears in the press here is the bad news.

This morning Coltart got a telegram from Mugabe which said in part: "As you are no doubt aware, we in the government intend to establish a nonracial society based on equality and the promotion of the well-being of all our people in accordance with our socialist principles. It is in this connection we have adopted our policy of reconciliation whereby our people must put aside the hatred and animosity of the past.

"I call on all of you who have completed your studies to return and join us in the urgent task before us. I hardly need to remind you that this is as much your home as it is ours. As has so often been said, in identifying and returning to the new Zimbabwe you have nothing to fear but fear itself. Yours sincerely, R.G. Mugabe."