London — With its commanding views of Nelson's Column and the National Gallery, the South African Embassy on Trafalgar Square occupies a prime piece of London real estate that is the envy of foreign diplomats.
Less prestigious to the South Africans is the prospect that next month, Trafalgar Square is likely to see an outpouring of anti-apartheid protesters.
The occasion is the lightning, but highly controversial, trip to London of Prime Minister Pieter W. Botha. Brief as the visit might be - it consists of an official working lunch on June 2 - the anti-apartheid demonstrators vow it will be a visit the prime minister will never forget.
News of British Prime Minister Margaret Thatcher's invitation to Mr. Botha has infuriated the opposition Labour and Liberal parties. The trip has been attacked as distasteful, inappropriate, and an insult to Britain's black community, which is 6 percent of the population.
Some critics have even gone so far as to say that inviting Mr. Botha to Britain is ''like inviting Hitler.'' The demonstrations, expected to be among the largest seen in Britain in recent years, poses yet another challenge for London's policemen, who are preoccupied with the need to guarantee the safety of Western world leaders when they arrive in London for a June 7-9 economic summit.
Botha's trip is part of an effort to reduce world isolation of South Africa that arose as a response to the white minority government's racial policies.
Despite the British opposition, South Africa is hailing the London visit as a significant breakthrough.
Mr. Botha's visit is being interpreted partly as a reward for pursuing a more outward-looking foreign policy. Nudged by America's southern African strategy of ''constructive engagement,'' South Africa has, in quick succession, signed a nonaggression treaty with Mozambique and a cease-fire with Angola. Direct talks with the South West Africa Peoples Organization over Namibian independence were held this month, although little came of them. Some of the rationale for the invitation is to help encourage Botha to continue gradual internal reform.
Botha's trip to London will be the first by a South African premier in almost a quarter of a century.
West Germany, Portugal, and Switzerland are also on his itinerary, but Britain will be the high point because of the strong historic links between the two countries.
Although South Africa is now a republic outside the Commonwealth, a small Union Jack has been retained in the South African flag as a reminder of the colonial past. Britons remain the largest immigrant group in South Africa, and there lingers a sentimental attachment in Britain to South Africa as a founding member of the Commonwealth.
But the British have a repugnance for South Africa's apartheid policies. London is a haven for Afrikaner renegades, South African English-speaking liberals, and African nationalists.
One of the items on the agenda at the June 2 meeting is certain to be South Africa's unhappiness with Britain for failing to take action against the African National Congress. In South Africa's view, the London headquarters of the ANC serves as the international nerve center for carrying out terrorism in South Africa.
The ANC and the Anti-Apartheid Movement have charged that South Africa is carrying out a concerted plan of dirty tricks against its London critics. Allegations range from misinformation and harassment to illegal arms deals, burglary, and bombing of the ANC office.
The British government's distaste for South African race policies has forced it to ban arms exports and to limit sporting contacts with South Africa. But British moral sensibilities do not extend to ending trade ties.
The Anti-Apartheid Movement regards Britain's refusal to stop trading with a country whose policies it has described as ''abhorrent'' as frustrating and hypocritical.
Until the 1960s, as much as 30 percent of all the business of British banks outside Britain was in South Africa. The United States and West Germany now are more important trading partners for South Africa than Britain, but trade between South Africa and Britain flourishes.
An official of Britain's Board of Trade Industry says Britain imported some (STR)765 million ($1 billion) in goods from South Africa in 1983. British exports to South Africa that year came to (STR)1.1 billion. By comparison, US exports to South Africa for 1982 topped $2.3 billion.
Anti-apartheid critics have argued that the only way South Africa can be brought to its economic knees is to suspend investment in and trade with the republic. So far no British government has been willing to pay the price.
According to the United Kingdom South Africa Trade Association, unemployment in Britain would increase by 250,000 if two-way trade links were cut.
The Anti-Apartheid Movement's charges of hypocrisy about Britain trading with South Africa are echoed by many South Africans. A South African Embassy official here claims that Britain indulges in double standards, forbidding amateur athletic sporting contacts but imposing no curbs on professionals.