JERUSALEM - Palestinian Prime Minister Ahmed Qureia said Monday he was ready for a summit with Ariel Sharon (news - web sites), but only if the Israeli premier agreed to move on some tough Palestinian demands, including halting the construction of a West Bank security barrier. Sharon said he would not accept preconditions for a summit, and the dispute threatened hopes for a decisive effort to end three years of violence and jump-start the stalled "road map" peace plan. Momentum seemed to be building in recent days toward such a push after the main Palestinian militant groups agreed to a...