LAGOS (Reuters) - Nigeria's central bank plans to offer $100 million in currency forwards on Monday to be delivered within the next 60 days, traders say. The bank has consistently been selling foreign exchange to importers since February in a move to increase dollar supply in the market and narrow the margin between official and black market rate. The local currency was quoted at 307.50 to the dollar on the interbank market at 1256 GMT compared with 307 a dollar closed on Friday, while it was quoted at 445 on the black market, firmer than 450 a dollar closed on Friday. (Reporting by Oludare Mayowa, editing by Pritha Sarkar)