VIENNA/DUBAI (Reuters) - OPEC will debate an oil output cut of 4.0-4.5 percent for all of its members except Libya and Nigeria next week but the deal's success hinges on an agreement from Iraq and Iran, which are far from certain to give their full backing.

Three OPEC sources told Reuters a gathering of experts from the oil producer group in Vienna had decided on Tuesday to recommend that a ministerial meeting next week debate a proposal from member Algeria to reduce output by 4.0-4.5 percent.

But sources also said the representatives of Iran, Iraq and Indonesia had expressed reservations about their level of participation in the proposed deal.

(Reporting by Alex Lawler and Rania El Gamal; Writing by Dmitry Zhdannikov; Editing by Dale Hudson)