Utah's Index of Leading Economic Indicators increased sharply during the first nine months of 1988, pointing to sustained economic expansion in 1989, First Security Corp. says. The September index, developed by First Security economist Kelley Matthews, was 4.5 percent above last year, as the index continues its pattern of month-to-month volatility. "This gain reflects real economic expansion, as the impact of inflation and seasonal factors has been removed," Matthews said. Individual indicators used in the Utah index include new automobile sales, new automobile loans, consumer loan delinquency rate, initial claims for unemployment, nonagricultural job placements, valuation for nonresidential construction permits, new dwelling unit permits, manufacturing workweek hours, and new Utah corporations.