NY -- Standard&Poor's CreditWire 1/28/98 -- Standard&Poor's today assigned its single-'A'-minus rating to Johnson County Unified School District No. 231, Kansas' G.O. refunding and improvement bonds series 1998-A. The rating reflects a steadily expanding local economy with proximity to the broad and diverse Kansas City metropolitan area and healthy assessed valuation growth. Offsetting factors include adequate financial performance and negligible reserves, and a high debt burden with further capital needs. Located in northeastern Kansas, the district serves the cities of Gardner, Edgerton, Antioch, and unincorporated areas of Johnson and Miami Counties. Population has risen over 40% from 1990-1997 to 11,778, due largely from out-migration of existing residents in the Kansas City metropolitan area seeking more affordable