THE MUZOREWA GOVERNMENT has now accepted the British constitution for legally independant Zimbabwe-Rhodesia. The Patriotic Front has not. That has created a genuine crisis at the Rhodesia conference in London. Happily, Prime Minister Margaret Thatcher is facing it with fortitude. She and her foreign secretary, Lord Carrington, are not buckling to the Front's pressure tactics. They are showing deserved confidence in the fairness of the proposed constitution and an awareness that to be intimidated is to lose vital momentum and authority. They have not closed the door on the Front -- quite the contrary -- but they are starting talks with the Muzorewa government to put the constitution into effect.

So this is the moment of truth for the front. It can spurn the constitution and keep fighting, a course that may -- not -- bring it total victory but that will surely complete the ruin of Zimbabwe, among other effects. Or it can accept the constitution and join the transition talks, taking a chance by submitting its fate to elections but figuring the country will gain. It would be good to think that the Front's friends, especially Zambia and Mozambique, which are paying an immense price for supporting the Front, will be urging the Front to go the political route. The British compromise also deserves full backing from all members of the Commonwealth. This is no time for wobbling.

The United States if on the diplomatic sidelines. Yet plainly, American help will be necessary at least to make the economic side of any settlement work. The Front evidently accepts the new constitution's formulas for political rights but has balked at an economic provision -- compensation of whites for expropriated land. What may be needed is not merely American money but American ideas. For like Parliament, Congress is likely to be reluctant to put up funds simply to buy out whites who wish to take the money and run.

In 1976, the Ford administration, in its Rhodesian initiative, had some interesting ideas that may be relevant still. It suggested that the longer white farmers stay, the higher should be their compensation: an incentive to stay and keep the economy going. It had some other development proposals centered on the special needs of a society recovering from sanctions and war. These ideas do bear the fingerprints of Henry Kissinger -- but surely that would not keep the Carter administration from dusting them off?