Fannie Mae and Ginnie Mae are seeking to protect taxpayers as a flood of new lenders apply to do business with them, but that is also helping big banks' profit and blunting Federal Reserve efforts to boost housing, Bloomberg News reported yesterday. Fannie Mae, the government-supported mortgage financier, has begun limiting how many loans annually it will guarantee or buy from certain firms. Ginnie Mae has moved slowly with responses to applications, according to David Lykken, an industry consultant. The U.S.-owned bond insurer has gotten tougher this year about approving lenders even as it is signed up about 50, Ginnie Mae President Ted Tozer said. Limited competition in the industry and a lack of capacity to meet demand is helping JPMorgan Chase & Co. Chief Executive Officer Jamie Dimon get “very high” mortgage margins. That’s frustrating central bankers such as William Dudley, the Federal Reserve Bank of New York president, who said this month that mortgage rates are higher than they could be after the Fed said that it plans to acquire $40 billion of home-loan securities a month.