FIRST GRANITE <FGBI> AGREES TO BE ACQUIRED First Granite Bancorp Inc said it agreed in principle to become a wholly owned subsidiary of Magna Group Inc <MAGI>. Under terms of the agreement, First Granite shareholders will receive 2.175 shares of Magna for each First Granite share held. First Granite shareholders will be asked to approve the tranaction in late summer. First Granite, which has 675,000 shares outstanding, as of Dec 31, 1986 had assets of 186.5 mln dlrs. It owns First Granite City National Bank and Colonial Bank of Granite City, Ill. Magna Groups as of Dec 31, 1986 had assets of 1.47 billion dlrs. It owns 13 banks, a data services company, a mortgage company and a trust company, serving St. Louis as well as Springfield, Centralia and Decatur, Ill.