Central bankers gathered here for the monthly meeting of the Bank for International Settlements have decided against putting together an official rescue package for South Africa, banking sources said today.

The rebuff was conveyed personally to Gerhard de Kock, governor of the South African Reserve Bank, who had traveled here to make the case for organization of an international consortium to reschedule his country's international debt in the face of its mounting financial crisis, the sources said.

De Kock was in Switzerland to meet Swiss bankers in the course of a 10-day odyssey that has taken him to the United States and Britain to discuss South Africa's financial problems. While the BIS, as usual, issued no statement after the regular meeting -- a spokesman refused even to confirm that De Kock had been present -- participants said privately that a general decision had been taken not to organize any financial "rescue" for South Africa.

"We think there is a need for major political reforms in South Africa before we get into any talk of a rescue package," one central banker said on leaving the meeting.

South Africa is a member of the BIS, which often is referred to as the "central bankers' central bank."

Meanwhile, banking sources in Zurich said De Kock was told by the three major Swiss banks -- Union Bank of Switzerland, Swiss Bank Corp. and Credit Suisse -- that Switzerland will not call in its current loans to South Africa, although it will not lend any additional money. This point already had been made by Robert A. Jecker, executive vice president of Credit Suisse, at a press conference last week while De Kock was in the United States.

Union Bank Chairman Nikolaus Senn said in a television interview today that "the South African economy is basically sound. This is not a Latin American country, and we are not worried about the safety of our loans there. It is really just a question of the South Africans resolving their credit problem."

Switzerland is the second-largest lender to South Africa after the United Kingdom, with loans totaling $1.5 billion in the period 1982-84, according to figures compiled by the World Council of Churches.