Fixed mortgage rates on long-term loans in the United States dropped marginally in the week ending Thursday, the Federal Home Loan Mortgage Corp. said. With prices not far above record lows, the average 30-year fixed mortgage dropped from 3.59 percent to 3.55 percent with an average 0.7 points, Freddie Mac said. A year earlier, interest rates for 30-year, fixed-rate loans were at 4.12 percent. For 15-year loans, interest rates held steady at 2.86 percent with an average 0.6 points. A year ago, 15-year loan rates averaged 3.33 percent. Interest rates for five-year adjustable-rate mortgages dropped from 2.78 percent to 2.75 percent in the week with 0.7 points. In the same week of 2011, rates for five-year ARM contracts stood at 2.96 percent. The average interest rates for one-year ARM contracts fell from 2.63 percent to 2.61 percent in the week with 0.4 points. Rates a year ago for one-year ARM contracts averaged 2.84 percent.