NY -- Standard&Poor's CreditWire 10/29/98 – Standard&Poor's today assigned its double-'A'-minus rating to Portage, Mich.'s special assessment bonds series 1998 dated Nov. 1, 1998 due Dec. 1, 2018 and GO limited tax city share bonds series 1998 dated Nov. 1, 1998 due Dec. 1, 2018. The bonds are scheduled to sell Nov. 3, 1998. In addition, Standard&Poor's affirmed its double-'A'-minus rating on the city's outstanding GO debt and on Portage Building Authority's outstanding bonds, issued for Portage. The rating reflects: -- Above-average income levels, -- Strong management, and -- A solid financial position. Mitigating these strengths are tax and employment base concentration and high carrying charges. Portage is located midway between Chicago and Detroit.