In a dramatic televised twist to a war that's over two years old, Bosnian Serb leader Radovan Karadzic, in a CNN interview, offered major concessions and asked for the mediation of Jimmy Carter to bring an end to the conflict. Karadzic said that effective tomorrow a cease-fire would be declared in the besieged city of Sarajevo and that U.N. flights would be allowed to enter its airport. He also agreed to release all Muslim prisoners under the age of 19, abide by international conventions on human rights, release U.N. personnel taken hostage to prevent NATO air strikes and allow free movement of U.N. convoys. Bosnian Serb leaders have made -- and broken -- some of these pledges to mediators. From Georgia, ex-president Jimmy Carter said he would wait between 24 and 48 hours to see if the Bosnian Serb leader will keep his promises before deciding to go to Sarajevo. Carter said he had briefed President Clinton, who Carter said was pleased but skeptical. As of now, a Carter Bosnia mission won't be on behalf of the Administration and it isn't clear that his visit would be backed by U.S. troops. If Karadzic keeps his promise it's likely to be a major breakthrough in the two-and-a-half year long war in the former Yugoslavia.