WASHINGTON (Reuters) - U.S. industrial production unexpectedly fell in October as output at power plants and mines declined, but a third straight month of gains in manufacturing suggested the economy remained on a moderate growth path. Industrial output slipped 0.1 percent last month after advancing 0.7 percent in September, the Federal Reserve said on Friday. The drop in October was the first since July. Economists polled by Reuters had expected industrial production to gain 0.2 percent. Manufacturing output increased 0.3 percent even as automobile assembly fell for the first time since July. Manufacturing output, which had edged up 0.1 percent in September, was supported by gains in the production of primary metals, furniture and computer and electronic products among others. The sector is regaining some momentum after hitting a soft patch early in the year. Utilities output fell 1.1 percent last month after surging 4.5 percent in September. Mining production contracted 1.6 percent in October, the first drop in seven months. The Fed attributed the fall to temporary shutdowns of oil and gas rigs in the Gulf of Mexico as Tropical Storm Karen approached. Last month, the amount of industrial capacity in use fell 0.2 percentage point to 78.1 percent. Industrial capacity utilization - a measure of how fully firms are using their resources - was 2.1 percentage points below its long-run average. Officials at the Fed tend to look at utilization measures as a signal of how much "slack" remains in the economy, and how much room growth has to run before it becomes inflationary. (Reporting by Lucia Mutikani; Editing by Chizu Nomiyama)