WASHINGTON (Reuters) - Hurricane Katrina is likely to have only a modest impact on the U.S. economy as long as the hit to the energy sector proves transitory, White House economic adviser Ben Bernanke said on Wednesday. "Clearly, it's going to affect the Gulf Coast economy quite a bit," Bernanke told CNBC television. "That's going to be enough to have at least a noticeable or at least some impact on the aggregate (national) data. "Looking forward ... reconstruction is going to add jobs and growth to the economy," he added. "As long as we find that the energy impact is...