NEW YORK, Oct 30 - The Chicago Federal Reserve Bank said on Thursday its gauge of the national economy turned positive in September, helped by renewed strength in production and a marked pickup in employment. The Chicago Fed's National Activity Index rose to +0.20 in September from a downwardly revised -0.40 reading in August. "The positive value for the index in September reflected renewed strength in the output-related data, a marked improvement in the employment-related data, and continued robust housing data," the Chicago Fed said. The three-month moving average of the index also improved, to +0.05 in September from -0.08 in August, the first positive reading since June 2000. Earlier on Thursday, the Commerce Department reported the U.S. economy grew at a blistering 7.2 percent pace in the third quarter.//