A TOUGH, tough challenge to Prime Minister Robert Mugabe of Zimbabwe: the leading radical in his fledgling administration, manpower minister Edgar Tekere, is now accused of the murder of a white farm manager. The man had complained that Mr. Tekere and some followers were making noise at a party, and the next day there was a shootout. If Mr. Mugabe is not seen to enforce the law impartially against his black colleague, the white exodus will likely become a rout, black factionalism may explode and international investment and aid will be scared away -- it could signal the end of all reasonable hopes for a revived multiracial Zimbabwe. If Mr. Mugabe is seen to enforce the law impartially, then immense problems will remain. But Zimbabwe has a chance.

Mr. Mugabe's image in the West as a guerrilla leader conceals the subtle reality that is at the heart of this cruel test. Mr. Mugabe was the political leader of a guerrilla-based political party. Mr. Tekere was a guerrilla leader, the man who fought in the bush. Mr. Mugabe emerged from the war with a vision, formed from his political experience, of what Zimbabwe needed in order to survive; it is, even many of his erstwhile white foes have since agreed, a large and humane vision. Mr. Tekere emerged with a loyalty to the particular creed -- essentially, a one-party, black, socialist, confrontational state -- that he had preached to his fellow guerrillas.

Now that the war in Zimbabwe is over, it's hard for Americans to keep track of what's going on there, but the Tekere case is sharp and significant enough to become a new focus of concern. The encouraging thing is that the old American debate over Rhodesia has almost entirely faded away. Those who formerly leaned to the Smith or Muzorewa regimes seem no less eager to see the new government work than those whose major emphasis used to be on bringing the guerrilla groups into the political picture. There is an almost palpable longing across the board to see Mr. Mugabe make it: to build a moderate multi-racial society and to keep the Soviets on the outside.We hope he does make it, and we hope that Congress will then realize the great American interest in helping him -- we mean aid.