* Import prices rise 0.2 percent on petroleum * Prices fall 1.0 percent from a year-ago * Export prices up for the first time since February By Lucia Mutikani WASHINGTON, Oct 23 (Reuters) - U.S. import prices rose for the second straight month in September as the cost of petroleum increased, but there was no sign of a build-up in imported inflation pressures. Import prices rose 0.2 percent last month after a revised 0.2 percent gain in August, the Labor Department said on Wednesday. Import prices had previously been reported as being flat in August. Economists polled by Reuters had expected prices would gain 0.2 percent in September. In the 12 months through September, import prices fell 1.0 percent. This likely reflects U.S. dollar strength earlier in the year. "Underlying inflationary pressures are limited in the U.S. and no risks of inflation spikes at the final stages of the price formation chain are expected anytime soon," said Annalisa Piazza, an economist at Newedge Strategy in New York. Import prices excluding petroleum were flat from August. Compared to September last year, they fell 1.0 percent, the largest drop since November 2009. The report was originally scheduled for release on Oct. 10 but was delayed after the federal government was partially shut down because of a fight over the budget. The 16-day shutdown ended last Wednesday. The government will release September wholesale and consumer inflation reports next week. NO INFLATION PRESSURES The general lack of imported inflation pressures against the backdrop of weak global demand and commodity prices should help the Federal Reserve to maintain its monthly bond purchasing program into early next year as it tries to nurse a lackluster economy back to health. Domestic inflation is also muted and will likely stay that way for a while as demand remains tepid. "The Fed has little to fear about inflation," said Joel Naroff, chief economist at Naroff Economic Advisors in Holland, Pennsylvania. "It is likely that quantitative easing will continue into next year." Last month, imported petroleum prices rose 0.8 percent after rising by a revised 1.9 percent in August. Imported food prices advanced 0.5 percent after increasing 0.3 percent the prior month. Elsewhere, imported capital goods prices were unchanged from August, as were prices for motor vehicles. Automobile prices fell 1.2 percent from a year ago, the largest year-over-year decline since records began in June 1981. The Labor Department report also showed export prices rose in September for the first time in seven months, posting a 0.3 percent gain. Export prices had dropped 0.5 percent in August. Export prices were lifted by agricultural goods, where prices rose 0.7 percent after steep declines the prior month. While agricultural export prices rose last month, they fell 6.3 percent from a year-ago. That was the largest year-over-year decline since October 2009. Prices for exported industrial supplies and materials rose 0.7 percent from August. There were also increases in the price of exported fuels, which advanced 0.7 percent. Exported capital goods prices rose marginally, while autos were flat.