BELGRADE — Heavy fighting continued Wednesday in the breakaway republic of Croatia, and Yugoslavia's collective presidency remained at odds over European Community (EC) efforts to prevent a full-scale civil war.Officials close to the presidency said Yugoslav President Stjepan Mesic, representing his native Croatia on the eight-man presidency, supported EC calls for a Yugoslav peace conference. The officials, who asked not to be named, said Mr. Mesic and Slovenian leader Janez Drnovsek accepted the idea of EC monitoring groups in Croatia to control a truce that went into effect Aug. 7 but has been continually violated. They said Bogic Bogicevic of Bosnia-Herzegovina, and Vasil Tupurkovski of Macedonia, were "close to Mesic and Drnovsek," while Borisav Jovic of Serbia and members representing Serbia's two autonomous provinces, could not agree without consulting Serbian communist leaders under Pr esident Slobodan Milosevic. At an emergency EC ministerial meeting in Brussels on Tuesday, foreign ministers condemned the Yugoslav army for siding with Serbian guerrillas in battles with Croatia's security forces. The ministers also asked Serbia to admit EC monitoring teams to Croatia, adding that if no agreement on the peace conference was reached by Sept. 1, the EC would consider unspecified international intervention.