S. African premier's European tour breaks 30 years of isolation

South African Prime Minister Pieter Botha begins a tour of Europe today prepared for dialogue - up to a point. Analysts here say Mr. Botha begins the tour open to an exchange of views on regional affairs in southern Africa - and that he may be susceptible to some European pressure on this subject.

Independence for Namibia (South-West Africa) is expected to be a key topic. But a chilly silence could descend if the Europeans urge Mr. Botha to abandon or rapidly overhaul South Africa's system of apartheid, which excludes the country's black majority from meaningful political rights, these analysts say.

Botha probably sees his European tour as a triumph over those who have sought to pressure South Africa's white rulers to make domestic changes, say experts on Pretoria's foreign policy approach.

Since the National Party came to power in 1948 South Africa has sought a formula for dealing with the outside world that would not threaten - and would even safeguard - apartheid, says Deon Geldenhuys, author of a recent book on South African foreign policy.

Past formulas fizzled. But now six European countries - Portugal, Britain, West Germany, Switzerland, Austria, and Belgium - have opened their doors, suggesting Botha's formula is working so far, Geldenhuys says.

The trip itself represents a reversal in South Africa's slide into isolation since World War II. Prime Minister Johannes Voster met US Vice-President Walter Mondale in Vienna in 1977, and Hendrick Verwoerd visited Britain in 1961. But Botha's degree of acceptance is far greater.

Botha first sought greater dialogue with the black states of southern Africa. Pretoria sought and got a nonaggression pact with Mozambique and agreed to a cease-fire in southern Angola.

The consensus here is that European leaders are receiving Botha primarily to reward him for his moves toward regional rapprochement and to encourage him to do more. The Europeans no doubt feel justified in meeting him when some black African governments who oppose South Africa have begun working with him.

Dialogue between South Africa and its black-ruled neighbors goes against the pattern of the past 30 or so years.

As independence began to sweep through Africa in the 1950s and '60s, relations between the former colonial powers and South Africa grew strained. As European governments recognized black rule in Africa, they found it increasingly difficult to do business as usual with Pretoria. South Africa's racial policies hardened, too.

Black Africa demanded that South Africa be isolated until it began internal reform. South Africa sought to improve ties with Africa and the West without internal concessions.

Botha, too, rejects demands for change within South Africa as a condition for more normal foreign relations.

Geldenhuys cautions against considering this European tour a ''turning point'' leading to South Africa's return to international respectability. But many analysts believe Botha may widen this opening to him by moving toward Namibian independence.