CONGRATULATIONS TO Bishop Abel Muzorewa, whose inauguration as prime minister of Zimbabwe Rhodesia ends nine decades of white minority domination. He takes over a government of uncertain authority at home and minimal acceptance abroad, a wracked economy and a war. Realistic assessments are required.

He should nip any tendency to think that if he hangs tough the United States and Britain will bail him out. Even if one lifts sanctions or moves toward recognition, trade and morale would not be sufficiently improved to make much difference. Nor is it possible to imagine that Western diplomatic support, let alone military aid, could become a saving factor. Some of his American supporters advise Bishop Muzorewa to "win" his war, but he should not be misled by the noise of American political debate into thinking that he will get much more than their good wihses. It is simply not in the cards. His friends owe him an honest judgment on this question.

Mr. Muzorewa could decide that with South African support, which is considerably more likely, he could win the war - especially if Rhodesia's whites let him make the domestic gains for blacks he must make to show he is not Ian Smith's boy. But could he win? Or would he and his government be destroyed in the process? And what would the country look like at the end of the war? The bishop, who has just made himself defense minister, needs to look directly at these questions. So do the American well-wishers who urge him to win the war.

For the United States, only one policy makes both political and diplomatic sense: to encourage democracy and peace at the same time. Herein lies the trouble with the Amercian debate so far. The Administration's critics have emphasized democracy; the fuss over the Case-Javits amendment, setting "free and fair" elections as a condition for lifting sanctions, has skewed discussion in that direction. The administration had emphasized ending the war, and in so doing has sometimes conveyed the impression it would prefer a victory by guerrilas who would impose a Marxist state.

In fact, democracy is important but, without peace, not possible to achieve. And peace is important - but, without democracy, less worth achieving. The administration and its critics must work out a common understanding on that ground. The United States as a nation would then be in a position to work, as events permitted, for accommodation. Unquestionably such a policy would be welcomed by the Front Line states. It would have a stronger chance of acceptance by the Rhodesian parties than any alternative in sight. It might, of course, fail. But the failure would clearly be the responsibility of the Rhodesian parties alone.