Under the Reagan administration's policy of ''constructive engagement,'' South Africa is finding it easier to obtain US-made products. The new policy, which has reversed two decades of increased restrictions on American exports to the white-ruled nation, has drawn criticism from members of Congress and religious and activist organizations.
In August a South African government-run research council took delivery of a powerful Amdahl 470/V7 computer from California, and a private Johannesburg firm received a shipment of 2,500 ''shock batons'' made in Florida. Both sales were licensed by the US Department of Commerce, which must approve exports to South Africa if they have potential nuclear or crime-control applications, or if they are going to government agencies such as the military and police.
The most controversial so far has been the shock baton sale, which was licensed in April but came to light only last month.
The story of how these electrified weapons got to Johannesburg involves a product demonstration at the State Department, complete with sample shocks; to an apparent bureaucratic foul-up at the Commerce Department; and a central figure in a scandal which toppled South African Prime Minister John Vorster three years ago.
The Commerce Department revoked the export license for the batons earlier this month, but with no hope of retrieving the goods.
The application to export the batons was made early this year by American International Marketing Associates of New Jersey. The firm's two partners, James O'Conner and Joe McCrane, said in an interview that they expected approval of the deal because of the adminstration's relaxed regulations on trade with South Africa.
Although the new rules have not produced a bonanza for American manufacturers , they have opened the way for some sales that would have been blocked in previous years. Three American aircraftmakers, for example, say they have been told by the Commerce Department they could compete for the sale of six turbojets - civilian versions of planes purchased by the US military - to the South African Air Force for use as air ambulances.
The Commerce Department has issued at least a dozen licenses, including 10 for computers or computer-related equipment, under what Commerce Secretary Malcolm Baldrige has called ''a more flexible policy'' on exports of dual-use, nuclear-related items.
The Amdahl computer sale to the Council for Scientific and Industrial Research (CSIR) in Pretoria is one of these, and so was Control Data Corporation's earlier sale of a sophisticated Cyber 170/750 computer to the same agency.
Although the application from the California-based Amdahl Corporation was processed more quickly, it, too, had to be reviewed by the National Security Council's Subgroup on Nuclear Export Coordination (SNEC), made up of officials from the Departments of State, Defense, Commerce, and Energy, and the Nuclear Regulatory Commission.
Because CSIR is involved in nuclear- and military-related research, as well as private and scientific study, some US officials were fearful that these large-capacity computers would enhance South Africa's nuclear development. Official US policy is to curtail nuclear ties until Pretoria agrees to complete safeguards for its nuclear facilities and signs the Nuclear Non-Proliferation Treaty.
The licenses for both sales to CSIR stipulate that neither computer be used in nuclear or military applications. Inspections are to be carried out by the manufacturers and American embassy personnel, after being prearranged with CSIR.
Manufacturers of the shock batons, meanwhile, set up a meeting at the State Department in March to boost the chances for approval of their application. While officials present took turns getting shocked, ''we explained how it appeared this was the right thing for South Africa because it doesn't hurt people,'' Mr. O'Conner recalled.
Known as the ''Source,'' the weapon sold to South Africa is described by the Florida manfacturer as a ''humane, effective, and nonlethal'' alternative to conventional crowd- and criminal-control equipment such as night sticks, blackjacks, high-voltage shock batons, and the ''Taser,'' a 50,000-volt dart gun used by many police departments, including those in Washington and Los Angeles.
Says Capt. James A. Smith, president of Universal Safety Corporation in Largo , Fla, ''(The shock baton) feels like a small bee sting. . . . This sensation simply causes a person to remove his hand without the officer having to use excessive and harmful force.'' He says the ''Source'' discharges a ''microcurrent'' that remains on the skin for less than a millionth of a second, too briefly to penetrate the body.
On April 26, a few weeks after the State Department demonstration, the Commerce Department issued a license authorizing export of 2,500 shock batons valued at $180,000. But news of the sale did not surface until Sept. 17, when congressional staffers discovered it on a computer printout of crime-control equipment exports supplied to the House Subcommittee on International Trade by the Commerce Department.
Officials at both the Commerce and State Departments say the license approval was ''an honest mistake,'' a ''simple, unfortunate'' foul-up. A low-level official in the Office of Export Administration at the Commerce Department approved the license application without the knowledge of his superiors and without consultation with the State Department, these officials state. When the case was brought to the attention of both departments by Congress, it was too late.
In August the 2,500 units had been shipped to Bonuskor, a holding company headquartered in Johannesburg and owned by the Afrikaner-controlled Volksas Group, South Africa's ninth largest corporation.
O'Conner and McCrane were first approached on Bonuskor's behalf by L.E.S. de Villiers, former deputy secretary of the Department of Information during the 1970s, when Information Minister Connie Mulder and Information Secretary Eschel Rhoodie were orchestrating a worldwide image-building campaign using secret funds. A scandal over allegedly misappropriated money swept the department, ruining both men's careers and leading to the resignation of former Prime Minister John Vorster.
Mr. de Villiers, who, according to the official inquiry into irregularities in the department, was in charge of ''some secret task,'' left the government in late 1977 before the investigation began. Later, he set up De Villiers' Inc. in New York.
Contacted by telephone, de Villiers asserted that the deal has been misrepresented in press accounts referring to ''cattle prods'' and ''torture instruments.''
But criticism of the sale continues. ''It is difficult to understand how such a mistake could occur,'' declared six members of the Senate Foreign Relations Committee in a letter to Commerce Secretary Baldrige.