High-level officials of the United States and South Africa met in unusual secrecy in Vienna yesterday after the Pretoria government made known its intention to inform Washington of "important decisions" soon to be made in that strife-torn country.

The U.S. delegation, headed by presidential national security affairs adviser Robert C. McFarlane, met a team headed by South African Foreign Minister Roelof F. (Pik) Botha at the U.S. Embassy in the Austrian capital. The two groups plan to meet again in Vienna today without McFarlane, who is flying home to report to President Reagan.

Officials here said a South African request last week for an "urgent meeting" suggested that a package of new measures and policy declarations is being considered to ameliorate the increasingly violent situation in that country and to placate the rapidly growing international reaction.

Officials said the Reagan administration, which took no action on an earlier request for a high-level meeting of the two governments, concluded early this week that the new approach from South Africa was positive and promising enough to justify such a session.

"We agreed to the meeting because of the importance of our having direct contact with the South African government at this tense time," said State Department spokesman Bernard Kalb. He added that "the meeting afforded us an opportunity to discuss the serious situation inside South Africa and in the region, a situation about which the administration has strong views."

Officials said the U.S. team, including Assistant Secretary of State Chester A. Crocker and Ambassador to South Africa Herman W. Nickel, went into the meeting ready to expound Washington's viewpoint on the causes and resolution of the deepening racial strife within South Africa. The State Department said again yesterday that the United States stands for "an end to the violence, the restoration of law and order, the lifting of the state of emergency and the resumption of the black-white dialogue."

Growing conflicts between Washington and Pretoria on regional questions, including a May 21 South African guerrilla raid on the Gulf Oil facility in Angola, were topics for discussion between the two delegations, according to U.S. sources.

"U.S. policy remains the same," said a White House official in response to questions about whether the U.S. delegation was prepared to acquaint Pretoria with any shift in the Reagan administration's embattled policy known as "constructive engagement." Other officials noted, however, that overwhelming congressional support for legislation containing economic sanctions against South Africa presents a new situation that must be taken into account in both capitals.

Botha, who was accompanied by Herbert Beukes, South Africa's ambassador-designate to the United States, was reported also to be meeting with senior officials of the British Foreign Office and other European governments.

Senate Foreign Relations Committee Chairman Richard G. Lugar (R-Ind.) said he received advance notice of yesterday's high-level meeting from Secretary of State George P. Shultz on Wednesday.

"We have been trying to get their [South Africa's] attention," Lugar said of U.S. policy, and "we're pushing awfully hard for changes to be made" that might reverse the deteriorating situation there. "I think we are at least initially encouraged that South Africa wants to make some changes and is ready to tell us about it before they do so."

There has been widespread speculation in South Africa that a regional meeting of the ruling National Party late next week will be the occasion for important announcements by Prime Minister P.W. Botha. Despite hopes that he will announce some remedial measures, Botha said yesterday in Pretoria that he could "introduce stronger steps" if there is no lessening of the violence.

Lugar said the coming weeks are likely to be unusually important for U.S.-South African relations because the Senate is expected in mid-September to break a filibuster holding up final congressional action on legislation that includes economic sanctions. The Foreign Relations Committee chairman said he hopes that President Reagan will take some initiatives to promote greater U.S. involvement on behalf of change in South Africa before the Senate vote. Lugar has urged Reagan not to veto the bill, which has support among both Republicans and Democrats in Congress, but said yesterday he is uncertain what the president will do.

The U.S. delegation to the talks with South Africa left here Wednesday without any public notice, nor was any announcement made in Pretoria or Vienna.

Spokesman Kalb made the meetings known only under heavy questioning from reporters. Foreign Minister Botha, asked by a reporter in Vienna to explain the main objective of the talks, replied: "I am not in a position to comment on that. You were not supposed to know I was here."

Face-to-face meetings between high-level representatives of the U.S. and South African administrations have been sparse in recent months. Washington called Ambassador Nickel home June 15 as a sign of displeasure with South African policy. Pretoria responded July 30 by recalling Ambassador Designate Beukes, who had been waiting here for weeks to present his credentials to the administration.