VIENNA — Austria is considering possible recognition of the rebel republics of Croatia and Slovenia if diplomatic efforts fail to avert civil war in Yugoslavia, Chancellor Franz Vranitzky said on Aug. 6.Mr. Vranitzky, in a statement of support for international efforts to end the crisis, said priority had to be given to stopping the conflict between Croatia and the rival Yugoslav republic of Serbia. "The Austrian federal government is considering the recognition of Slovenia and Croatia as an option. This can be realized at the same time as other states," Vranitzky said. His statement followed similar remarks Monday by the German government and appeared to rule out unilateral Austrian recognition. Some 300 people have been killed in ethnic violence in Yugoslavia since Croatia and Slovenia declared independence June 25. No country has formally recognized the two republics, which were part of the Austro-Hungarian empire until 1918. Vranitzky said only international efforts appeared likely to head off a war in Yugoslavia and welcomed a proposal by French Foreign Minister Roland Dumas to involve the United Nations Security Council.