Utah's index of leading economic indicators declined sharply in February, dropping 1.6 percent below the January figure, First Security Bank of Utah said. The level was the same as in October 1988 when the index fell 1.4 percent below the previous month's total. Bank officials said the February decline doesn't appear to be part of a general weakening trend in the Utah economy, but they are anxiously awaiting the results of March data. They said the growth momentum in Utah's February index, which narrowed to 0.3 percent, was the slowest annual growth in more than two years. The Utah index takes into account automobile loans, new automobile sales, the consumer loan delinquency rate, unemployment claims, nonagricultural job placements, nonresidential and residential construction permits, manufacturing workweek hours, and new Utah corporations.