A new air gloom settled over South Africa today with the news that Prime Minister John Vorster and Vice President Walter Mondale mained seriously divided after two days of talks in Vienna.

the outcome described in banner headlines here as a "Sharp Split" and a "Head'on Collision," has blacks and whites to express concern about the possibly loss of Western support at a critical point for their controversial isolated than at any previous time.

Most political commentators here saw the meeting as a "last chance opportunity" for the two countries to agree on terms for a united front against what is viewed as the growing "red treat" to African. The initial public reaction today is that those hopes were dashed.

There was also serious concern expressed about the implications of Vorster's defiance of U.S. pressures for a "full participant" by blacks in government here.

The attitude of many whites was reflected by an Afrikans winery owner: "It 's back to the vorlaaier," - the musket used by his 17th Century Dutch ancestors during the days of early settler conflicts with Africans.

Both moderate and conservative whites said today that it appeared South Africa would indeed now have to go it alone to defent itself against increasingly militant black governments, as the prime minister has been warning since the truth of the year.

For blacks, the breakdown - as it is interpreted here - is seen as a signal that there is no hope fo significant changes in their condition.

A black schoolteacher from SoWet, Johannesburg's troubled African township. commented: "This is the saddest day in my Life. In effect, he (Vorster is inviting more confrontations. He is not losing just American support."

"We have been looking to this day to find out how serious the government is about changes. about coming to terms with us. Now we know."

The timing of Vorster's defiant stand in favor of continued racial separation could indeed by the final spark to fuel a new outburst of disorders.

There have already been rumors about demonstrations scheduled for June 16, the anniversary of the first riots in Soweto. Many students have talked about new protests over last week's banishment of Winnie Mandale, wife of imprisoned black nationalist leader Nelson Mandale, from Soweto to a remote township.

The prime minister may have an ticipated the possible reaction, for on the eve of his departure for Vienna he held talks in Cape Town with Soweto police chief Jan Visser, according to an Afrikaans newspaper here.

In a front-page editorial, the liberal Rand Daily Mail warned that the "tough Mondale declaration of American intention" at the conclusion of the talks puts South Africa "into an entirely new era" in both its international and domestic relations. The editorial suggests that South Africa "will all be well advised to take a cold, hard look at the new situation in which we now find ourselves."

The fact that there was agreement between Vorster and Mondale on peaceful means of establishing black majority rule governments in Rhodesia and Namibia (Southwest Africa) received relatively little attention here, for both steps were anticipated before Vienna meeting.

What South Africans really wanted to know was whether Western support for the troubled Vorster government would be worth the stiff price tag: Basic changes in South Africa's political structure. As they learned today, it was not.

A black business commented tonight: "Vorster has taken his stand as he said he would. There is no chance that he'll back down later. The Afrikaner rarely does."