HOUSTON, Aug 18 (Reuters) - A U.S. judge on Monday

authorized a court officer overseeing an auction of shares in

the parent of Venezuela-owned refiner Citgo Petroleum to receive

and negotiate improved bids this week before confirming or

changing the winner recommendation he made last month.

A final winner recommendation in the complex court-organized

auction is expected to be submitted by the end of this month,

Judge Leonard Stark said in a hearing.