U.S. residential mortgage originations will likely drop to $1.46 trillion in 2006 from $1.49 trillion in 2005, the Mortgage Bankers Association estimated Wednesday. In its economic forecast, the group also said existing home sales will probably fall by 4.7% in 2006 and 4.4% in 2007. New home sales will likely drop 4.3% in 2006 and 4.9% in 2007, the group added.