THE VIOLENCE IN Rhodesia is sickening. Defenseless European missionaries are being murdered in numbers, apparently by guerrillas intent on intimidating the rural population and undermining the government's control of the countryside. Government forces have taken to killing scores of Africans by firing mass volleys into village groups suspected of being hostile.

The war's weekly death toll is now estimated at 100; if Rhodesia had the population of the United States, the figure would be 3,000. In seven years some 9,000 people, mostly, Africans, have been killed; that's upwards of 270,000 on an American scale. Last month two Swiss and an African performing the civilizing mission of the International Committee of the Red Cross were found dead outside their marked van, shot in the back of the head. It is not possible to tell which side is more responsible for the spreading savagery.Both are responsible.

In Britain, some of the Conservative opposition, aroused by atrocities against British missionaries, suggest that the carnage should be laid at the feet of the Labor government. If the government had embraced the settlement fashioned by Ian Smith and the "internal" black nationalists last March, the argument goes, the "external" nationalists would not have been encouraged to fight on and the war would be winding down now. There are similar incipient mutterings in the United States.

But that line of argument is simplistic. It should not have to be demonstrated, after Vietnam, that guerrilla wars cannot be turned off or on in foreign capitals. The guerrillas wish to demoralize their foes and, specifically, to render unfeasible the elections that constitute the one means by which the Salisbury administration could validate its claim to popular acceptance. The internal people have largely failed to persuade the guerrillas to put down their arms and they must now try to defeat them in the field. Cruel as it is, that is the political logic of the war.

One result that the widening war ensures is that the country the victor inherits will be an African Lebanon, a disaster area in terms of human and political relations and probably in terms of economic viability, too. A political compromise along lines suggested by the United States and Britain is the one conceivable way to diminish the violence, but as Salisbury's position becomes more desperate, the Popular Front's seems to harden. That is a formula for more killing.