According to a survey published in the Los Angeles Times, retail gasoline prices climbed only slightly over the last three weeks, leading forcasters to predict that prices will come down after the late-summer spike.During the three weeks ending on Sept. 12, the national average price for self-serve regular gas rose 0.14 cent per gallon, averaging $1.7205 per gallon, according to the Lundberg survey of 8,000 gas stations. This indicates a stabilizing of prices after the 15-cent jump in prices during the two-week period ending on August 22.According to Trilby Lundberg, editor of the survey, there were two main reasons for the spike in prices. First, the power outage in the eastern U.S. interupted production at some refineries. Second, a temporary shutdown of a pipeline in Arizona reduced supplies in several areas.The 15-cent hike in August was the largest increase recorded in the 50-year history of the survey, Lundberg noted. According to the survey, the highest average price for self-serve regular gasoline was in the San Francisco area, where it ran $2.11 per gallon. At the other end of the scale, the lowest average price was found in Atlanta, GA, where it cost $1.45 per gallon.