SOUTH AFRICA'S latest attack into Lesotho, the weak little independent black nation it completely surrounds, was an inexcusable act of bullying. Utterly dependent on Pretoria's whim, Lesotho is well known for trying to avoid giving South Africa the slightest pretext for querying its policy. It has perennially restricted anyone who might be an activist or guerrilla of the African National Congress, the leading (outlawed) black nationalist organization in South Africa. None of the accounts now coming out of Lesotho supports South Africa's claim that the 40-odd victims of its commando attack were recently arrived ANC terrorists planning to undertake new missions soon. Most of the victims were refugees, including some women and children, and the others were Lesotho citizens.

If the threat was unconvincing, what did South Africa's white minority government actually have in mind? To keep guerrillas from operating in any of the black nations on its border, it seeks to dry up support available to them among refugees and nationals in those countries. Beyond that, it wants to build up a row of buffer states subservient militarily and in other ways. In this spirit, South Africa has sent its troops on regular, large, punitive raids into Mozambique and Angola, supported local guerrilla challenges in both of those countries and perhaps incipiently in Lesotho as well, and otherwise acted to weaken and divide its neighbors.

There is a terrible cycle at work here. South Africa has yet to convince its black majority that its system of legal racism known as apartheid offers them even a chance of dignity and equality. Denied legal or political recourse, black nationalists go underground, often fleeing abroad. The South African government then seizes upon their activity, or simply their innocent presence, to punish them and the countries where they live.

It is difficult even for members of the white opposition in South Africa to stand up against military operations launched in the name of fighting ANC terror. Fortunately, the Reagan administration found its voice and sharply criticized the attack, observing correctly that such violence underlines the urgency of political solutions.