Bankers in Montana have won the right to sue the federal government for  letting a credit union expand to serve a 3,600-mile area in the western   part of the state.   
Following a two-year-old precedent set by the U.S. Circuit Court of  Appeals for the District of Columbia, Judge Charles C. Lovell ruled March   31 that a group of seven banks could sue to roll back Missoula Federal   Credit Union's 1992 expansion.     
  
The National Credit Union Administration argued that bankers didn't have  the right to sue because the Federal Credit Union Act was not designed to   protect banks. The judge ruled that banks still had a stake in the agency's   actions.     
The banks have "a competitive interest in limiting the expansion of MFCU  pursuant to the common bond provision," wrote the judge for the U.S.   District Court for the District of Montana.   
  
The banks sued the regulator in September 1993.