A group of shareholders that includes former senior executives of its  banks is demanding that Maryland's Mason-Dixon Bancshares consider selling   itself.   
The group includes the former chief financial officer of the company's  original bank, Carroll County Bank and Trust Co., Westminster, and the   founders of Bank of Maryland, Towson, which Mason-Dixon bought last year.   
  
Members of the group hold a 5.1% stake in Mason-Dixon and have banded  together as Anthony Investments Inc. to mount a proxy challenge. 
Anthony Investments claims that the company's independence benefits only  current executives and board members - not shareholders. The firm reported   its holding of 268,671 shares to the Securities and Exchange Commission   last week.     
  
The 17 shareholders have also issued a proposal they want included in  the 1997 proxy statement that would ask shareholders whether Mason-Dixon   should be sold.   
Former Bank of Maryland chairman Hildebert F. Criste and fellow founders  Charles A. Miller Jr. and Clarke Langrall are in the group. Bank of   Maryland was started in 1985.   
Mason-Dixon officials said they're not going to meet the group's demands  to shop the bank around. 
  
"We don't believe that is in the best interests of stockholders, to  deviate from the company's strategic plan - which is to remain   independent," said Thomas K. Ferguson, president and chief executive.   "We're absolutely committed to that plan."     
To plead its case, the company ran a large advertisement Tuesday in The  (Baltimore) Sun addressed to shareholders and customers. 
Mason-Dixon, which has $836 million of assets, is one of the few  remaining Maryland banking companies of significant size. The Carroll   County unit is the market leader in its growing rural area west of   Baltimore.     
But in its SEC filing, Anthony Investments said the bank is not  performing as well as its peers. 
  
Barbara S. Floyd, president of Anthony Investments, Severna Park, Md.,  could not be reached for comment. She is a former chief financial officer   of Carroll County Bank and Trust.   
Mason-Dixon's Mr. Ferguson said Mason-Dixon's return on equity - 12.27%  for the six months ended June 30 - was diminished by its 1995 acquisition   of $230 million-asset Bank of Maryland. The peer ROE average during that   time was 13.28%.     
An analyst who follows Mason-Dixon stock said the group might be jumping  the gun in challenging management on performance grounds. 
"It just strikes me as a little early in the game to start screaming,"  said Alex C. Hart, a bank analyst at Ferris, Baker Watts Inc.