There are more and more signs that the Reagan administration's policy of ''constructive engagement'' with South Africa is not bearing fruit. This new approach was based on the thesis that the US could accomplish more by not preaching at South Africa about its repugnant racial policies. Instead the US would mute its public criticism, adopt a friendlier tone, and thus - it was hoped - encourage Pretoria to be more forthcoming, both at home and abroad.
There does not appear to be any response to this. Despite some modest advances toward alleviating racial conditions in South Africa, harsh treatment of blacks continues, detentions are on the rise, and reports persist of physical abuse in the prisons. Then there is the critical issue of Namibia (South-West Africa) which, for all the ''constructive engagement'' with it - still seems to elude solution. The war goes on, despite years of Western effort to end it and to negotiate the independence for Namibia called for by the UN.
Has US strategy gone wrong?
Many knowledgeable people think the administration has greatly underestimated South Africa's determination to resist change. Moreover, by agreeing in effect to link a Namibia settlement with a pullout of Cuban troops from Angola, it has given South Africa the pretext it most needs for stonewalling a withdrawal from Namibia and continuing its military actions in Angola. At the United Nations this week Angolan Foreign Minister Paulo Jorge called the US preoccupation with the Cubans ''a kind of paranoia.''
Of course the Cuban presence in Angola, as elsewhere in Africa, is a concern. From the standpoint of the Luanda government, however, the Cubans provide a shield against the insurgent forces of Jonas Savimbi and the South African forces backing him. The great fear is that, if the Cubans are pulled out prematurely, the US will not be able to stop a South African-Savimbi drive to oust the Angolan regime. Mr. Jorge claims that South Africa now has 5,000 soldiers in Angola. Luanda, in other words, seeks to avoid a full-scale civil war.
It may be difficult to take at face value Mr. Jorge's statement that Angola will reduce the number of Cuban troops when South African forces are cut back. But, given the fact that South Africa has a long history of bringing up red herrings to block a Namibia agreement, Angola's skepticism about South African intentions is understandable - especially when Pretoria has the support of influential right-wing forces in the US.
The administration perhaps needs to rethink its position on connecting a Namibia settlement with the Cuban issue. It should be obvious in Washington that the South African government, politically weak now, does not want to arouse South Africa's own right wing by giving up Namibia. The South African military, for its part, has never been keen about a settlement.
Yet much is to be gained for the West by resolving the Namibia question. This would eliminate the last remaining colonial problem which the Russians can exploit in southern Africa and thus help bring stability to the region. With the South Africans out of Angola, it would enable the contending political forces there to work out their own future. Not least of all, it would free South Africa of an enormous financial drain and enable it to focus on its own internal problems.
It would also be a feather in President Reagan's cap. Having made what seems to be appreciable progress on basic details of a Namibia agreement, it would be a pity if this were all undermined by a failure to compromise on the Cuban troop matter - and by an unwillingness to bear down harder on South Africa. If soft talk does not work, perhaps it is time something else was tried.