The Mortgage Bankers Association says U.S. mortgage activity rose marginally in the week ended Friday with long-term mortgage rates steady or falling. Interest rates for 30-year, fixed-rate mortgages were unchanged in the week at 4.29 percent with points rising from 0.38 to 0.41, the trade group said. Rates for 15-year, fixed-rate contracts fell from 3.52 percent to 3.46 percent with points increasing from 0.38 to 0.45, the association said. The banking group said its weekly mortgage activity index rose 0.6 percent while the refinancing index rose 2.2 percent.