* Israel believed to be Middle East's sole nuclear armed power * US and Israel see Iran as region's main proliferation threat * US, UK hopeful on meeting on Middle East free of nuclear arms (Adds vote outcome, quotes) By Fredrik Dahl VIENNA, Sept 25 (Reuters) - Member states of the U.N. nuclear agency on Thursday rejected an Arab resolution targeting Israel over its assumed atomic arsenal, in a diplomatic victory for the Jewish state and Western countries opposing the initiative. ...