Some of the biggest U.S. banks have been cooped up within the confines of New York City, forbidden by state law to set up branches or holding companies to buy banks in the fast-growing suburbs of Westchester and Nassau counties. Efforts of Manhattan bankers to change the law have always been blocked by a coalition of small-town Republicans and solid Democratic opposition in the state legislature. Among the caged banking Goliaths: the Chase Manhattan (assets: $8.5 billion), whose vice chairman is David Rockefeller, brother of New York's Governor Nelson Rockefeller.
Last week, at the urging of Brother Nelson, the state...