President Carter confirmed yesterday he is sending Vice President Mondale on a second international diplomatic mission, a nine-day, five-country trip to Europe that begins May 14, and includes a meeting with South African Prime Minister John Vorster in Vienna.

That meeting, tentatively scheduled for May 14, will be the first direct contact between top Carter administration officials and the nation that Carter has said "is a stablilizing influence in the southern part of that continent," and has a "major role to play in the peaceful resolution of Rhodesia and Namibia."

Administration sources see the meeting as part of a three-pronged approach toward evolving a United States African policy.

The American mission to the United Nations confirmed yesterday that U.N. Ambassador Andrew Young will make a second visit to Africa around May 9 for about two weeks.

A spokesman said there are no plans for Young to meet with South African officials, but he will confer with U.S. ambassadors to African countries at a "Chiefs of Missions Conference," and attend a U.N. decolonization committee meeting in Mozambique the third week of May.

Sources said President Carter is also expected to discuss southern Africa in general and Rhodesia in particular with British officials during the London summit conference that begins Friday.

Mondale's trip will take him to Portugal, Spain, Austria, Yugoslavia and Great Britain, where he is also expected to confer with British officials about southern Africa.

His schedule calls for him to meet Young in Lisbon May 15. Young would presumably fly in from Africa.

Mondale's late January trip cast him in the role of the first emissary from a new and unknown U.S. President to meet the leaders of Japan and the major European industrial nations.

This time he will hold the administration's first meetings with Austrian Chancellor Bruno Kreisky and Yugoslavia President Marshal Tito.

Carter said in a statement that Mondale "will continue the important consultations we have begun with the Portugese and Spanish governments." Portugese Prime Minister Mario Soares and Spanish President Adolfo Suarez have met Carter at the White House.