Utah's index of leading economic indicators declined in December for the second consecutive month, according to Dr. Kelly Matthews, senior vice president and chief economist for First Security Corp. He said the indicators declined 0.6 percent in December, a different direction than the national figures that inched upward. He said that a drop in the index doesn't indicate a decline in the state's overall economy. The December index was 154 (1978\ 100), which was 0.8 percent below the same month's a year ago. No other two consecutive monthly declines have occurred since early in 1989.