For years experts have criticized regulators for the complex rules they devise to control large financial institutions. Now officials at the FDIC, the Federal Reserve, and the Office of the Comptroller of the Currency have proposed simple rules requiring higher levels of capital by large banks. And the move, while less stringent than that proposed recently by Sens. Sherrod Brown and David Vitter, would leave some banks scrambling to strengthen their capital positions. For instance, JPMorgan Chase alone would have to raise its position by $50 billion.