Death squads kill South African opponents. Pretoria appears to have shifted tactics in battling the African National Congress. In what some call `terrorizing the terrorists,' death squads are taking a toll on ANC members in nearby countries.

The undeclared war between South Africa's rulers and the outlawed African National Congress appears to have entered a new phase in which ANC cadres and even sympathizers are assassinated by mobile death squads in neighboring states. Although Pretoria is widely believed to be responsible, it denies any involvement.

Strikes against the ANC by faceless assassins have been most marked in Swaziland, a tiny kingdom that ANC guerrillas have used as a conduit to and from South Africa. Thirteen men and women, most of them known or suspected members of the ANC, have been gunned down there in the past nine months. Similar attacks have occurred recently in Mozambique.

ANC casualties in Swaziland include Cassius Make, a member of its national executive and a high-ranking commander of its underground army, Umkhonte We Sizwe (Spear of the Nation). Shortly after arriving in Swaziland by air last month, Mr. Make and another ANC operative, Peter Motau, were forced off the road and shot dead in broad daylight. The ANC blamed ``South African agents.''

Earlier this month, two more men were eliminated in what looked like the latest episode in the secret war between ANC fighters and South African agents. The two were living inconspicuously in the servants' quarters in a house in the Swazi capital of Mbabane, having entered Swaziland last month. They were killed when a gunman brazenly walked down the driveway in the morning and fired a fusillade of shots through the door into their room.

In the past, there have been both attacks by suspected South African agents operating incognito and ``preemptive'' raids by uniformed South African security force commandos - such as the June 1985 cross-border attack on alleged ANC targets in Botswana and earlier attacks in Lesotho and Mozambique.

The past year has seen what appears to be a shift toward the use of agents, with nearly all attacks - and kidnappings - being carried out by unidentified men.

A well-placed source in South Africa describes the use of incognito agents as a highly effective method of ``terrorizing the terrorists.''

Assassins operating in the shadows, this source says, can strike at any time, creating a perpetual sense of unease, whereas raids by commandos were usually followed by a lull during which ANC fighters could breathe easy again.

Moreover, the source adds, agents can strike more quickly and precisely, thus reducing the risk of acting on out-of-date intelligence and thus killing or wounding innocent civilians.

There have also been abductions of suspected ANC leaders in Swaziland by unidentified men.

The most notable kidnapping was that of Ebrahim Ismail Ebrahim, a former political prisoner and alleged regional ANC guerrilla commander. Now on trial for treason relating to his alleged role in planting land mines on South African territory near the Swaziland border, Mr. Ebrahim was kidnapped late last year by unidentified men described by his lawyer as ``agents of the South African state.''

His kidnapping took place shortly after South Africa's foreign minister, Roelof Botha, publicly acknowledged that Pretoria's agents had kidnapped ``ANC agents'' from Swaziland late last year to forestall a long-planned attack on South Africa. At the time, Mr. Botha warned that South Africa would launch a raid against the ANC in London if South African security were at stake.

Since then, four men have appeared in court in London on charges of conspiring to kidnap British-based leaders of the ANC. Two of the purported conspirators are expatriate white Zimbabweans.

Hard on the heels of Ebrahim's appearance in a South African court came the decision of a Botswana court to jail for five years a British national, Steve Burnett, for attempted murder of a South African anti-apartheid activist, Ronald Watson, in a Botswana hotel. During the trial, Mr. Burnett claimed to have been a member of Britain's crack Army antiterrorist unit, SAS (Special Air Service). Mr. Watson told the court that Burnett had boasted that he was working ``in conjunction with South African security.''

Actions against the ANC by men suspected of having ties with the South African security forces are not new. As far back as 1981, the chief ANC representative in Zimbabwe, Joe Gqabi, was shot dead by an unidentified gunman. In 1982 Ruth First, wife of the general secretary of the South African Communist Party and ANC executive member Joe Slovo, was killed in a parcel bomb explosion in Mozambique. In 1984, ANC sympathizer Jeanette Schoon and her young daughter Katryn were killed by a parcel bomb in Angola.

More recently, assassins equipped with silencers attacked ANC targets - in Lesotho in 1985 and in Maputo, Mozambique, last May. Nine people were killed in the Lesotho attack, six of whom were ANC members or sympathizers. Three Mozambican nationals died in the May raid.

The ANC is taking the intensification of the ``war in the shadows'' seriously. ``South African hit squads have been very active,'' says Solly Smith, the ANC's chief representative in London. ``They are going all out.''

The ANC labeled the use of faceless hit squads a form of ``state gangsterism,'' charging that the South African government was forced to deploy them because of its ``political bankruptcy.''

There have, of course, been casualties on both sides in the ``war in the shadows,'' with mobile agents or suspected agents of the ANC carrying out hit-and-run attacks against ``traitors'' and members of South Africa's security forces.

The murder last year of David Lukhele is one example. A black South African, Mr. Lukhele favored the Pretoria-backed plan of ceding the South African tribal territory of Kangwane - together with blacks deemed to be its citizens - to Swaziland.

Others include the 1984 murder by ANC insurgents of black activist Ben Langa, suspected as an informer; the 1982 killing of a black security policeman, warrant officer Philip Selepe; and the assassination in the black township of Soweto in December 1982 of an alleged ANC regenade.

There have also been ANC bombers whose targets are not so precise and whose victims, like those of South African commando raids, usually include innocent civilians.

Journalists in South Africa operate under official press restrictions. 30-{et