THE PREMISE of the latest British effort to negotiate a settlement of the racial conflict in Rhodesia is that the situation has changed since January, when the latest effor collapsed. It's an understandable premise. True, in the battlefield, things are about the same: Guerrillas are inflicting painful but far from crippling losses on tth whites, who can probably hang on for some time. The British have a few new wrinkles in their diplomacy but nothing to alter the basic cause of its ineffectiveness, national weakness. There is, however, a new American President, one who, though untested, starts with a certain credibility among black nationalists. This is what lends interest to the newly announced American readiness to co-sponsor a fresh conference on Rhodesia, if the British (as expected) decide to convene one, and to participate in its actual work.

Given the evident American unwillingness to offer more than words and some money, which is what the last administration offered to no avail, it has to be asked, nonetheless, what purpose will be served by a more prominent American role. It is all very well for Washington to proclaim a commitment to Africa's wellbeing, to peaceble settlement of disputes, and to multiracialism. But will this slow down the guerillas, who may feel that by fighting they can reap all the power rather than just a share? Will it induce Ian Smith to entrust the white community's welfare to "guarantors" far from the scene and demonstrably reluntant to act? It is worth a trip to Geneva merely to hold the British government's coat a new conference?

In fact, a conceivable result of the British-American approach to an "international solution," one including the guerrillas based outside the country, is an intensified drive by Mr. Smith and Bishop Abel Muzorewa to reach an "internal solution," one made with "moderate" blacks at home. Last January, Secretary of State Vance, new in office, dismissed "the so-called internal solution." But suppose Mr. Smith and the Biship, who is not a puppet but a politician with broad popular support, hatched a quick-majority-rule plan that allowed participation in internationally sanctioned electionseven by the guerrilla elements now proscribed. And what if the probable alternative was a sequence beginning with a new conference and ending in a rout of whites, a black civil war, and economic ruin?

Perhaps it will turn out for the worse whatever is now done. But we think there is ample reason to encourage Mr. Smith and moderate nationlists to try to make it come out better, if they can.