Prime Minister Margaret Thatcher said tonight that she saw "no reason and no evidence" for believing that economic sanctions against South Africa would lead to peaceful change there and warned that they "could make the violence worse."

Under increasing pressure from Britain's partners in the 49-nation Commonwealth to impose sanctions against Pretoria, Thatcher did not rule them out and said that she would consult with other western and Commonwealth leaders before making a final decision.

But in an interview with Independent Television News here, she gave no indication that she had changed her opposition to sanctions on the grounds that they "don't work." Asked if she was willing to risk a rupture in the Commonwealth by standing alone on the issue, Thatcher said, "If I were the odd one out, and I were right, it wouldn't matter, would it?"

As the single largest source of foreign investment in South Africa, and its third largest supplier of imports, Britain plays a crucial role in the South African economy. Its participation would be a central element in effective sanctions against Pretoria.

But for sanctions to be effective in influencing the government there, Thatcher said, "they would have to be applied by the whole western industrialized world, and others." Even then, she said, they could make the current violence in South Africa worse and, for blacks, "could add hunger on top of all the other things they have to deal with."

Full sanctions also could ruin the economic future for any fully democratic, representative government that might be achieved there.

Other considerations, Thatcher said, were the state of the world economy, and the level of world need for South African-supplied commodities, including platinum. She also said that 120,000 jobs here depend on Britain's economic relationship with South Africa.

In response to Thatcher's comments this evening, opposition Labor Party leader Neil Kinnock, who supports sanctions, said that "it is obvious that she is prepared to be wrong and vain, even if it means cracking the Commonwealth." Kinnock, who predicted that Thatcher soon would "start to move" under pressure, charged her with "appeasement of apartheid."

The House of Commons is scheduled to debate the sanctions issue next week. On Aug. 2, a special Commonwealth committee of seven leaders, including Thatcher, is due to meet in London to discuss possible new action against Pretoria. The basis for that discussion will be a Commonwealth report, released yesterday, warning that a bloodbath costing millions of lives may be imminent in South Africa unless effective economic measures are taken.

In a related development, the special envoy of the Archbishop of Canterbury, Terry Waite, postponed a trip to South Africa after Pretoria's embassy here retracted what he said was a promised visa today. Waite said that Ambassador to Britain Dennis Worral told him that after consultation with Pretoria, he could only grant the visa next week.

Waite has undertaken a number of foreign missions for the archbishop, Robert Runcie, including negotiations that led to the release of British prisoners in Libya, and unsuccessful efforts to free hostages held in Lebanon.

Waite said Runcie had asked him to go to South Africa to consult with Anglican Bishop Desmond Tutu and other church leaders and to investigate reports that church figures were being detained under emergency regulations announced yesterday.

Citing the expected increase in unrest in South Africa this weekend and on Monday, the 10th anniversary of the uprising in Soweto township in which hundreds of blacks died, Waite said the government in Pretoria did not want outsiders in the country who could make an objective report about events.