* Some Arab states willing to police the region themselves * raids seen as message to Qatar to stop backing Islamists * Arab states increasingly active in each others' crises * UAE and Egypt deny involvement, U.S. backs off statement (Adds State Department statement) By William Maclean DUBAI, Aug 26 (Reuters) - Air strikes against Libyan Islamist militants that U.S. officials had said were staged by Egypt and the United Arab Emirates could mark an escalation of a regional struggle over the future of the Arab world. ...