Mercantile Bancorp., which announced it would buy a sizable thrift in  its hometown of St. Louis, was the only major bank to stir the calm of   holiday trading last week.   
Since announcing Tuesday that it was purchasing $9 billion-asset  Roosevelt Financial Group, $18.2 billion-asset Mercantile saw its shares   gain just 63 cents to $50.125 as of Friday's close. Over the week,   Roosevelt's shares rose just 0.14%, to $20.625.     
  
Banks ended a week of light trading off a  bit. The S&P Bank index lost 0.06% to 468.45 while the Nasdaq bank index   gained 0.16% to 1,267.4. The Dow Jones industrial average was up 0.22% to   6,560.91.     
"The banks are holding up very well in the market, and the mood is still  very positive among the banks," said Charles Johnson, head of trading at   Blaylock & Associates. "There is some profit taking, but that just presents   some opportunities to buy shares in a more favorable way than usual. The   first quarter of 1997 will be a good one."       
  
The news of the Mercantile-Roosevelt deal surprised some investors, who  suspected St. Louis-based Magna Group Inc. - another active midwestern   acquirer - to be a more likely purchaser of Roosevelt. The news of   Mercantile's purchase boosted Magna's shares to $28.625.     
"A merger with Roosevelt, which would have been a merger of equals,  would have doubled Magna's size in Missouri," said Gerard Cronin, an equity   analyst with John Hancock Funds.   
In the past three years, Magna, a $6.6 billion-asset institution, has  acquired 44 banks throughout Missouri and Illinois and recently expanded   its reach into Iowa with its purchase of Homeland Bankshares in Waterloo.   
  
"The potential risk is that Missouri banks who want to remain  independent feel compelled to acquire under the assumption that size alone   will help them do that," said Mr. Cronin.   
"The risk in doing that is that it dilutes the ownership position.
G. Thomas Andes, Magna's chief executive, said his bank will continue to  grow through acquisitions, and maintained the bank's preference to remain   independent for the time being.   
"Our strategy is not just to get bigger, but to get better," he said."
  
Several analysts said several banks outside of Missouri - including Banc  One Corp., First Bank System, and Norwest Corp. - are possible purchasers   of Magna.