Vice President Mondale's impulsive call for "one man, one vote" in South Africa not only stunned and unified this nation's embattled white population but also strengthened the hand of bitter-end champions of racial separation.

Prime Minister John Vorster still has not fully recovering from the shock of his Vienna meeting with Mondale last month. Nor has much of white South Africa. That encounter brought home the change in U.S. policy under President Carter, vigorously supporting black African states who demand virtual white surrender to the black majority.

This impels the verkrampte (intractable) right wing of the ruling Nationalist Party to go "into the laager " - to form an armed camp against the rest of the world rather than attempt desperately overdue racial reforms. Since that is where the verkramptes wanted to go in the first place, moderate forces are anguished by the American blundering.

Certainly Vorster appeared to have gone "into the laager " when we were granted a private meeting with him this week at his office in the parliament building. The stern, forbidding prime minister would not permit direct quotation, but it can be reported he feels the Vienna meeting was important only in showing where he stands with the U.S. government.

Vorster returned from Vienna bitter that Mondale did not respond to Vorster's request for spelling out what the U.S. means by "full participation" politically of South Africa's black majority but then issued his "one man, one vote" call at a press conference. In the absence of any contradition from Washington, Vorster assumes Mondale's is the official U.S. position.

And although Mondale reflexively chose his words without authorization, the U.S. embassy here will not retract them. Indeed, the opinion of top U.S. diplomats here is that toughness forces South African concessions, such as its recent steps toward independence for South West Africa (Namibia).

But that view is rejected by practically everybody else (including some experienced hands at the U.S. embassy). Rather, Mondale's words have united white South Africa as at no other time during nearly two centuries of struggle between Afrikaaners and British. Since "one man, one vote" connotes the end of the white civilization here, South Africa's whites unite in self-preservation. Even the most liberal whites, members of the Progressive Reform Party, attack Mondale's formulation.

The political impact is pervasive. Leaders of the moderate opposition United Party, now in a state of dissolution, told us that they have lost still more voters to the Nationalists, R. F. (Pik) Botha, the new foreign minister who was expected to moderate the Nationalist Party caucus, has been pushed to the right, attacking Mondale and Andrew Young. Verkrampte Nationalists shout defiance from the benches of parliament.

Mondale's words climax South African grievances against Washington that began when the U.S. Congress pulled out of Angola, leaving South African troops high and dry fighting the Cuban expeditionary force. Moreover, the Vice President's words in Vienna coincided with Young's visit here, which, contrary to U.S. press reports, upset white South Africans far more than it reassured them.

Nor is this resentment limited to government circles. A U.S. Foreign Service officer, traveling through rural areas north from Cape Town into the Orange Free State shortly after the Vienna confrontation, discovered anti-American hostility he had not imagined. The hostility is all the more intense coming from a people who socially and culturally have copied Americans rather than Europeans.

The significance, many South African liberals believe, is that it discourages significant attacks on the institutionalized evil of apartheid. "All we are doing now is advocating the overthrow of the South African government without providing the money or force to accomplish it," one distraught and dissident U.S. diplomat confided.

The source of this policy is exposed by U.S. rejection of a proposed multi-racial solution for South West Africa, which had been viewed by moderates as a long step forward (though 30 years tardy) with implications for South Africa itself. The U.S. vetoed it for one key reason: opposition from black African states. In other words, U.S. policy is geared not to encouraging reform here but to courting the rest of the continent.

Accordingly, U.S. policy demands majority rule even if that requires political self-immolation by the white minority. The result is the whites' going "into the laager " - and a potential racial Armageddon. Although that is precisely what South Africa's militant young blacks want, whether it is the proper course for U.S. policy is a matter of grave doubt.