THE precondition for progress at tomorrow's scheduled European Community peace conference on Yugoslavia, said Lord Carrington, is a halt to the fighting and a will on all sides to reach a settlement. Without that the talks at The Hague are virtually certain to bog down.The former British foreign secretary and NATO secretary general was speaking as he prepared to chair the first session of the EC peace bid. "I can't see anybody sitting around a table while this fighting is going on being capable of looking objectively or dispassionately at what is happening." His remarks were made against a background of rising violence in Croatia and amid signs that armed clashes might be about to spread to the neighboring territory of Bosnia-Herzogovina. The aim of The Hague conference is to bring together leaders of the Yugoslav republics and convince them of the need for a negotiated settlement. Carrington is a seasoned negotiator who unraveled a civil war 12 years ago, in Rhodesia, now called Zimbabwe. He accepted an EC invitation to chair The Hague conference Tuesday. "You can't have a peace conference at which people don't want to agree. If there is a will on all sides to reach a settlement, that means people making concessions to the other side," Carrington said. But officials helping him to prepare for the talks said yesterday that renewed violence in Yugoslavia did not mean the peace conference would have to be postponed. "The hope is that the first session will be held, but what happens then will depend on the Yugoslavs themselves. It will certainly be impossible to make progress against a background of violence," Carrington said. After his help in settling the Rhodesian civil war, a leading commentator said of Carrington: "[he] has the art of banging heads together in the nicest possible way." Mikhajlo Crnobrnja, Yugoslavia's ambassador to the EC, thinks similar bilateral meetings and plenary sessions will be needed at the Yugoslav peace conference. "All the Yugoslav republics will be represented, and Lord Carrington will have to hold full sessions of the conference. But there must also be a lot of bargaining in the corridors," Ambassador Crnobrnja said. Carrington seemed to confirm that he would adopt that approach, and take initiatives of his own. "On Saturday we shall know a good deal more when we hear from the republics themselves about how they see the future," he said. "I think one can help to ease the passage of an agreement by proposing options and solutions." Ambassador Crnobrnja has been encouraged by the speed with which the EC was able to convene a peace conference and by Carrington's willingness to chair it. "We now have a framework which allows for peaceful mediation and for considering the legitimate grievances of the contending parties," he said. "All the points of tension in Yugoslavia can be brought into the open, in an atmosphere in which we are facing each other in the presence of EC mediators," he added.