NY -- Standard&Poor's CreditWire 5/27/97 -- Standard&Poor's today has assigned its `A-3' short-term counterparty rating to the National Bank of Greece S.A. (NBG). The rating reflects the bank's size and powerful position in the Greek financial markets, its strong liquidity, and its comprehensive rehabilitation program being implemented by the bank's management. At the same time, NBG's creditworthiness is somewhat constrained by weak profitability, asset quality and capitalization. NBG is the largest bank in Greece and holds a prime position in the country's financial markets, maintaining a dominant market share in both deposits and lending. This position and the loyalty of its customers have afforded it a very stable and relatively inexpensive funding base. NBG enjoys close