The South African government intensifies its campaign of force and threat against its neighbors. Just in the last few days, its armed forces, claiming to be attacking guerrilla bases, invaded neighboring Botswana's capital and coldly killed some 14 persons, including three women and a 5-year-old child. Then Pretoria proceeded with its long- rumored plan to set up a pliant puppet regime, its alternative to internationally acceptable independence, in its longtime colony of Namibia.

The attack on Botswana makes plain why the existence of apartheid in South Africa is itself a source of danger to the region. South Africa has made no showing that African National Congress guerrillas were operating out of Botswana. It simply stormed in, strewing about death, ntending presumably to add one more mark of intimidation to all the others that have made life miserable for its neighbors over the years. The imperial arrogance of South Africa, its determination to flaunt its uncontested power, was on full view. But what it really demonstrates is the lack of self-confidence, the insecurity, that lie not far under the readiness to go to the gun.

South Africa has spent decades failing to deliver on its promise to grant independence to Namibia, also a neighbor. In the Carter period, it went the puppet-regime route, which led nowhere, and now it is trying again. There is always a fancy excuse; this time it is that Cuban troops remain in Angola, to Namibia's north. But what South Africa does not say is that Cuban troops remain there to protect the Angolan government precisely against South Africa. Last month its commandoes were caught about to sabotage the American-owned oil facility that is Angola's most valuable economic asset. Meanwhile, Pretoria continues to sponsor the Angolan insurgency led by Jonas Savimbi. The same lack of self-confidence is evident: a fear of the fact and example of self-rule by blacks not beholden to South Africa.

The United States responded to the raid into Botswana by calling the ambassador home. It boycotted the installation of the new setup in Namibia, which it had already denounced as null and void. The question is not whether these protests are right and sufficient, however. The question is why South Africa proceeds with policies -- its repression at home as well as acts outside its borders -- that trash the expressed opinions and urgings of the government whose favor is most important to it. It proceeds with them, moreover, as Congress contemplates sanctions.

The evident answer is that South Africa has taken the U.S. policy of "constructive engagement" as a big wink. The policy was supposed to earn President Reagan a South African hearing for his counsel to reform but, regrettably, what it has actually brought seems much closer to contempt. What a pity that the president, in his unconvincing defense of administration policy last night, could not recognize that fact.