ROME — The F.A.O. Food Price Index edged downward in November, sliding to the lowest level since October 2010. At 192.6 points, the index, compiled by the Food and Agriculture Organization of the United Nations, was down from 192.7 in October and was the lowest since August 2010. The index is down 19% from the August 2011 high of 238. The F.A.O. cereal price index rose 4.7 points in November to 183. Cereal prices were still down 11.3 points (5.8%) from a year earlier. The November increase was the first significant monthly gain since March 2014. Falling in value in the November global index were dairy prices, down 3.4%, and sugar prices, down 3.2%. Vegetable oil prices were higher for the month and meat prices were nearly unchanged.