IAN SMITH, leader of the white-minority Rhodesian regime, has made his final move. He has abandoned the British-guided, American-supported effort to reach an "international solution" including the guerrillas based outside the country and organized loosely in the Patriotic Front. Instead, he has called new elections to seek a mandate for an "internal solution," presumably to be made with Bishop Abel Muzorewa, by all accounts the most popular politician in the country, or with Ndabaningi Sithole, another moderate nationalist, or with others. In a fair election, it is generally acknowledged, the guerrilla forces could not win.

In the past, Mr. Smith has avoided the internal route out of doubt that, even if the bishop and others stomached the "puppet" charge and accept ed it, the Western powers and neighboring African states would accept it and thus the guerrilla war would go on. He may also have wihsed to give Britain and the United States the opportunity to demonstrate that they could somehow moderate the Patriotic Front. But the Organization of African Unity unanimously endorsed the Front two weeks ago, dealing the back of its hand to Bishop Muzorewa. Mr. Smith found himself being asked by Britain to accept proposals reflecting the Front's determination to take power by the gun. The internal gambit is his response.

Secretary of State Vance just after taking office, derided the "so-called internal solution." To Ambassador Andrew Young, the principal guerilla leader is "my brother Rober Mugabe." British and American officials have reasoned that only by trying to draw the Front into the political process was there any chance of weaning the guerillas fron Communist influence and tactics, and of averting a complete breakdown in Rhodesia. But the OAU stand toled a virtual death knell for the BritishAmerican approach.

Much remains to be seen about the latest Smith plan. Is it more than a maneuver to reunite his own fragmented party? Will the Muzorewa-Sithole combination be able to use its new leverage to assure blacks a fair role in a new government and in the society at large? Will the Front be given the opportunity to take part in elections? It's a long shot. But if Mr. Smith gives good answers to questions like these, then London and Washington will have to consider supporting him. To continue encouraging the geurrillas, if majority rule is available to blacks by a fair internal democratic process, would be untenable. The larger problem would then be how to treat the situation created by guerrilla opposition to a government that, by virtue of dealing justly with blacks, would no longer a "rebel" regime.