American-made computers exported to South Africa in recent years have gone to government agencies engaged in defense research and arms manufacture, administrative boards that keep track of black population movements and, in at least one case, to a middleman who promptly reexported the sophisticated computer for delivery to the Soviet Union.

These exports have come despite regulations banning sales of computer equipment to apartheid-enforcing agencies and to South Africa's military and police forces. The exports suggest to officials at major American computer companies and in the U.S. governmment that new restrictions proposed by Congress will have little direct impact on the level of computer trade between the two countries.

What happens to the computers once they reach South Africa is a gray area, and it is impossible to document in most cases that they are being used for police, military or apartheid-enforcing purposes in violation of a ban imposed by former president Jimmy Carter.

The case of the computer that was reexported to the Soviet Union came to light only when it was intercepted in West Germany, but the middleman reportedly has disposed of other American-made computers that have not been traced.

Computer sales to South Africa have become an important political issue in Washington in recent weeks, with Congress set to impose formal restrictions on these exports as part of a package of economic sanctions against the South African government of President Pieter W. Botha. The Reagan administration, which is opposed to most of the sanctions, has suggested that it will impose its own restrictions on computers if President Reagan vetoes the sanctions bill.

Officials at computer companies and in the executive branch said they expect the newly formulated restrictions to have little more than symbolic impact on a trade that has begun to decline significantly in recent years. Company officials said they expect to continue their sales much the way they do now.

"Rather than have every minority in this country up in arms, Reagan will make it sound like he's cracking down, but then the word will probably get passed not to get too tough on any computer companies," a computer company official said.

The U.S. share of the computer industry in South Africa has dropped from 70 percent to 48 percent in four years, despite a relaxation of controls on exports by the Reagan administration in 1982.

Michael Dutton, a public relations official at International Business Machines Corp., which is the leading U.S. company in sales to South Africa, said many South African clients have "become nervous" about the possibility of sanctions being imposed.

"A lot of our business is shifting to foreign competitors, especially the Japanese," he said.

Reagan appears to be trying to limit the negative impact of his expected veto of the sanctions by having aides emphasize that he will ban computer sales to government agencies in South Africa that administer the strict racial segregation called apartheid.

This appears to be a reaffirmation of existing policy, since the Reagan administration already says it abides by Carter's 1978 ban on computer sales to apartheid-administering agencies. The sanctions bill bans nine South African government agencies from purchasing U.S. computers, parts and services.

The 1978 ban by the Carter administration prohibited the sale of any type of computer to the South African police and military. In 1982, the Reagan administration said it would approve sales of personal computers and communications equipment to the police and military as long as the equipment "did not contribute significantly to the military or police functions."

The Commerce Department also said export of computers destined for most South African agencies would be considered favorably if they were not to be used to enforce apartheid.

This June, Reagan reinstated for one year the Carter administration ban, but, according to an official at the Commerce Department, major changes have not occurred to limit computer sales.

"We're all looking into the new regulations carefully, but we're just not sure what changes will occur. In my opinion, in the area of computers, things will remain pretty much as they've been," the official said.

Antiapartheid groups charge that the regulations are written in imprecise language, allowing room for a great deal of flexibility. They also say inadequate enforcement and verification procedures allow some computers to reach agencies administering apartheid and the police and military.

"How do you really determine which government agencies are administering apartheid and which are not?" asked Thomas Conrad of the American Friends Service Committee.

"The whole government of South Africa maintains apartheid but in different ways. IBM can say it sold a computer to a local government agency that keeps track of taxes or electric bills or collects statistics on population. In my mind, that's helping the government to maintain the apartheid system."

Throughout the 1970s and in the early 1980s, IBM equipment was used in the South African Department of Interior to keep information on whites, Coloreds and Asians. Dutton said IBM no longer provides equipment to this department, because "we felt we may be using the equipment for repressive purposes."

IBM does supply computers to the South African government's Department of Statistics, and the computers are used for gathering civil service data, he said. Some antiapartheid groups charge that these computers have potential to do administrative work to maintain the apartheid system.

Dutton said that IBM equipment is used at a South African school called Technikon, which Conrad said has trained some police computer operators. Dutton said, "It is possible that the police register there as students, but to the best of our knowledge, there is no specific or special police training program."

Burroughs Corp. and several other computer companies sold equipment in the late 1970s and early 1980s to the some of the 14 government boards that issue permits and controls over the movements of blacks. Burroughs spokesman Irving Geller said Burroughs took its computers out several years ago, but Conrad said Burroughs was listed in the South African publication Computer Users Handbook as receiving rental fees from one such board in the early 1980s.

Sales of computers that are useful for nuclear weapons development have been made to a government-sponsored research council, according to an article placed in the Congressional Record by Rep. Howard Berman (D-Calif.).

One such computer was sold by Control Data Corp. to the government's Council for Scientific and Industrial Research in 1982, after the export controls were relaxed. One branch of the research council is the National Institute for Aeronautics and Systems Technology.

Robert Duncan, senior vice president of corporate marketing at Control Data, said the computer was purchased for research not related to nuclear, military or defense matters, but he acknowleged that Control Data cannot be completely certain that the aeronautics division does not use the computer.

In 1981, Sperry Corp. sold a computer to Atlas Aircraft, a subsidiary of South Africa's Armaments Corporation, the weapons development agency. A spokesman for the company said that as far as he knew that was the only sale it had made to Atlas.

Spokesmen for the eight major American computer companies operating in South Africa said they require purchasers to sign certificates stating the purpose the computer will be used for and promising not to use it for any agency that would violate U.S. regulations.

They said they are able to monitor the computers' usage through maintenance checks. "We have ongoing relations with our clients," said Barbara Kommer, a public relations official at Hewlett-Packard Co., which had $51 million in South African sales in 1984.

Government and company officials acknowledge that there is a potential for abuse in having the company monitor the client.

"It's not really our policy to tell our customers how to conduct themselves," said IBM's Dutton.

He said that it is the job of the government to enforce the regulations controlling computer sales in South Africa.

However, there have been some incidents that indicate the government agencies regulating these computer sales have made mistakes.

In 1983, the Commerce Department approved the sale of a Digital Equipment Corp. computer for export to South Africa. The equipment was later confiscated by U.S. officials in West Germany, where it was being diverted for use in Moscow.

According to many press reports, one branch of Commerce was investigating the company, run by West German Richard Mueller, that had applied for a license. However, another branch of Commerce, unaware that the investigation was going on, granted the license.

Digital Equipment, a computer company based in Massachusetts, said the equipment was sold to Saxto, a New York-based computer broker, which in turn sold the VAX computer to Mueller's company.

Digital Equipment official Joseph Nahil said the company was not penalized for that transaction but agreed to pay $4.1 million in fines to the Commerce Department for other dealings with Mueller. Nahil emphasized that the company had admitted no wrongdoing.

Commerce Department officials accused Digital Equipment of supplying 80 different high-technology products to Mueller through its West German subsidiary between 1981 and 1983.

Despite the incidents, the Commerce Department granted Digital Equipment a full two-year renewal of its distribution license.

A Commerce official said significant steps have been taken to improve coordination among governemnt offices so the Mueller incident is not repeated. He also said that the Office of Export Administration, which issues licenses, has "very substantially strengthened" its auditing and enforcement functions.

But, according to Conrad of the American Friends Service Committee, the administration's export policy is still "full of loopholes" and will allow "questionable activities" to continue.

"The sales made from subsidiaries or third parties are so unregulated that companies can continue to supply banned agencies or get involved in questionable activities without taking the blame," he said.

The American companies counter that they have more influence by operating in South Africa and supplying jobs to black workers.

In April, John F. Akers, chief executive of IBM, said, "We believe we are a force for change, and we are not going to leave." But IBM's rhetoric has become sharper since a state of emergency was declared a month ago in South Africa.

Spokesman Dutton said, "IBM is very concerned about the deteriorating state of affairs in South Africa. IBM believes economic activity can generate positive social change but such change is possible only when there is a commitment to overcome injustice. We believe the South African government should take the necessary steps for meaningful change to occur."