More than 90 percent of foreign investment in South Africa is accounted for by five nations -- Britain, the United States, West Germany, France and Switzerland -- according to an informal survey of information available from foreign governments, the United Nations and other international agencies.

The survey also makes clear that, at a time when many nations are grappling with proposals to ban new investment in South Africa until it changes its segregation policies, relatively little precise data is available on actual levels of investment.

It is apparent from the survey that Britain is by far the largest single investor in South Africa.

But the government of Prime Minister Margaret Thatcher, while condemning Pretoria's apartheid policies, has made clear that it does not believe that economic sanctions will work and has indicated that it would not take part in any western move in that direction.

The West German government also opposes economic curbs, and President Reagan has continued to voice his view that such sanctions will make things worse for South Africa's black majority.

However, three events in the past two weeks -- the decision by France to freeze new investments, the recall of the ambassadors of the European Community to consider joint future action, and the move last week by the U.S. Congress to force American economic sanctions -- have focused new attention on the murky question of who invests in South Africa and how much.

South Africa itself does not provide a country-by-country breakdown of investors but reports investment by region.

Officials at the South African Embassy in Washington said they had no figures on investment and refused to discuss the subject.

However, John Chettle, director for North and South America at the South Africa Foundation in Washington, said, "The South African government no longer issues those individual country figures for political reasons. I believe they feel that it enables groups to bring pressure on individual countries."

An advance copy of a report expected to be published soon by the U.N. Commission on Transnational Corporations says that at the end of 1983, the total amount of foreign direct investment in South Africa was in the range of $15.5 billion to $17 billion.

This represents about 10 percent of the country's total investment, the report said. An additional 20 percent of capital stock was held by foreigners in portfolio investment.

Foreign direct investment is substantial in sectors such as petroleum, motor vehicles, chemicals, electronics and banking.

The U.N. report said that in 1984, there were 1,068 transnational corporations with subsidiaries in South Africa. About one-third were headquartered in Britain, while firms based in West Germany and the United States each made up one-quarter of the total.

Based on this and a number of reports and interviews, The Washington Post has compiled the following information about investment and trade in South Africa.

*BRITAIN: South African ties to Britain go back to the 18th century, when British settlers started arriving at the Cape of Good Hope, and strong ties still exist between the two countries. In March, the British news magazine The Economist reported that British companies are by far the biggest corporate investors in South Africa. They account for about $8 billion, or half the $16 billion worth of direct foreign investment in the country, The Economist said.

A 1981 report of the U.S. Study Commission on U.S. Policy Toward Southern Africa, funded by the Rockefeller Foundation, estimated that British investment was responsible for 55 percent of total direct investment, or $8.7 billion.

Britain has more than $14 billion invested directly or indirectly in South Africa, according to the British Department of Trade and Industry.

Britain's investment in South Africa is about 10 percent of total British foreign investment, according to a survey on Britain by the Financial Mail, a South African publication, in November 1984.

Britain ranks third in trade with South Africa, following the United States and Japan.

In 1984, South Africa exported $742 million to Britain and imported $1.66 billion, according to the International Monetary Fund's 1985 Direction of Trade Statistics.

Unlike U.S. policy, which is neither to encourage nor to discourage investment, the British government actively promotes British business interests in South Africa.

The Thatcher government has said often that economic sanctions will not work and will harm those they are supposed to help.

Experts say that the British economy would be hurt by sanctions, which could aggravate the country's 13.5 percent unemployment rate.

The number of British jobs directly dependent on South African trade is about 150,000, according to John de St. Jorre, in a recent article in Africa Notes, published by the Georgetown University Center for Strategic and International Studies.

*UNITED STATES -- The United States is the second leading investor in South Africa, with between 18 and 20 percent of total direct investment in the country, according to a number of different reports.

U.S. direct investment in South Africa has gone from $490 million in 1966 to a peak of $2.6 billion in 1981 to $2.3 billion at the end of 1983. South Africa accounts for about 1 percent of total American foreign investment, according to the Investor Responsibility Research Center in Washington, which describes itself as a nonprofit research body on issues of corporate and social responsibility.

The U.S. State Department calculated a direct investment figure for 1983 of $2.3 billion and $7 billion in portfolios, for a total direct and indirect investment of $9.3 billion.

While figures vary, "the trend seems to be toward a decline in U.S. investment by businesses," said Chettle of the South Africa Foundation, an agency based in Washington representing South African businesses.

"The big U.S. companies I've talked to have told me without exception that they will remain in South Africa, but the smaller companies seem to think the harassment is not worth the candle," he added.

The United States is South Africa's largest trading partner. Last year, South African exports to the United States were worth $1.45 billion and imports from the United States totaled $2.37 billion.

A report by the congressional Republican Study Committee in May said that about one-fifth of U.S. imports from South Africa consist of gold coins, or Krugerrands. The Treasury Department estimates that total 1984 imports of Krugerrands came to $600 million, about 50 percent of South Africa's Krugerrand exports.

On July 31, U.S. House and Senate conferees agreed on a package of economic sanctions against South Africa, including a ban on the import of Krugerrands and a halt to new U.S. bank loans to South Africa.

The House approved the package two days later by a vote of 380 to 48, but the bill was tied up in the Senate. Action will be taken in September, when Congress reconvenes.

The legislation says that all sanctions could be waived if the president finds, and Congress agrees, that South Africa has taken one of several steps toward ending apartheid.

But if South Africa does not make progress within a year, the president would be required to recommend stiffer sanctions for congressional approval, including a ban on new private U.S. investment.

Chettle said, "I very much regret the actions taken by Congress, but I think the economic effect won't be very great. However, the symbolic damage in relations is much more important."

*WEST GERMANY -- About 10 percent of total foreign investment in South Africa comes from West Germany. West Germany's direct investment in South Africa in 1983 was $1.4 billion, according to the South African Embassy in London.

Investment by West German-based companies jumped about 30 percent in 1983, mainly because of increased investment in the automobile industry, according to the report by U.N. Commission on Transnational Corporations.

In the area of trade, the International Monetary Fund said that in 1984, South African exports to West Germany were $676 million and its imports were $2.3 billion. West Germany was South Africa's fifth-largest customer, behind the United States, Japan, Switzerland and Britain.

The result of economic sanctions would be the loss of 130,000 jobs in West Germany, according to the Institute of European Economic Studies in London.

*FRANCE-France is said to make up between 5 and 10 percent of total foreign investment in South Africa. In 1984, total French foreign investment there was $1.66 billion and represented 10 percent of total direct investment, according to the French Embassy in Washington.

Two weeks ago, the French government announced a freeze on new investment in South Africa and the recall of its ambassador.

In the trade sector, South African exports to France in 1984 totaled $385 million and its imports from France came to $568 million.

*SWITZERLAND -- Most experts estimate that about 5 percent of total direct investment in South Africa is Swiss.

The South Africa Trade Association in London reported that in 1982, total Swiss investment in South Africa was $1.34 billion.

According to de St. Jorre, Switzerland is important to South Africa because of its market for gold (almost half of the the country's gold exports pass through Zurich) and because of its financial resources for loans.

*CANADA -- Canada's direct investment in 1984 was $99.9 million, down from $140 million in 1983 and $148 million in 1982, according to Clifford Garrard, political counselor at the Canadian Embassy in Washington.

The Canadian share of total foreign investment in South Africa was 1 percent, he said, noting that the trend seems to be toward a decline in investment.

"I think all the unrest in South Africa is a major determining factor. It's a deterrent to investors," he added.

Garrard said Canada does not offer Canadian businesses investing in South Africa the support structures it normally offers companies investing abroad.

*JAPAN -- Japanese policy prohibits direct investment in South Africa but does not prohibit Japanese companies from establishing subsidiaries there.

De St. Jorre noted: "By the early 1970s, all of Japan's major trading companies had established outlets in South Africa, and many of its car, motorcycle, tire and electronics manufacturers had franchised local companies to assemble their products."

South Africa exported $1.3 billion to Japan and imported $1.9 billion in 1984, according to the IMF.

*OTHER ECONOMIC ASPECTS -- Denmark and Sweden have banned new investment in South Africa, and the Dutch parliament has been debating a similar measure. The four leading Dutch banks stopped selling Krugerrands in the spring.