Bank of Granite Corp., a North Carolina bank touted by super-investor  Warren Buffett, signed an agreement to acquire a mortgage banking company. 
Bank of Granite expects to complete its purchase of privately held GLL &  Associates, Winston Salem, by yearend. The mortgage company has offices in   Charlotte and three other North Carolina cities.   
  
Charles M. Snipes, president and chief executive of Bank of Granite,  said the acquisition would more than double the bank's mortgage operations.   "It gives us an opportunity to expand our mortgage lending into adjoining   areas and diversify our operations," Mr. Snipes said.     
Officials for the $508 million-asset bank declined to discuss the  purchase price but said the mortgage company would add to its earnings in   the beginning of 1998.   
  
GLL & Associates specializes in loans to first-time homebuyers in North  Carolina and has a niche in FHA and VA mortgages.