Secretary of State Warren Christopher called Wednesday for carrying out a negotiated settlement for Bosnia in ways that take into account "the needs" of the Serbs and other ethnic groups. It was Christopher's first change of position since the Dayton peace agreement was initialed November 21. "For a long time, Christopher and Richard Holbrooke had this insistence that this agreement was final and they weren't going to change a word," says TIME's Bruce Nelan. "While this may not signal a changing of the agreement, it is an acknowledgment that there are some things that still need to be clarified." Chief among these, Nelan says, is how Serbs will be treated when Muslims take over control of Serb suburbs in a united Sarajevo. "The Bosnian Serbs have been asking for guarantees that there won't be any Muslim reprisals against them. But providing specific guarantees is problematic. After all, keeping the sides from fighting is in large part this is what the peacekeepers are over there to do." Another Bosnian Serb concern, Nelan notes, is the fate of Serbs indicted as war criminals. Christopher said these issues will loom large in a conference of Allied and Balkan countries scheduled for Friday in London.