* Sales drop 0.3 percent in March from February * Energy and chemical products drag down sales * Statscan introduces historical revisions to data OTTAWA, May 15 (Reuters) - Canadian manufacturing sales sagged in March following an unexpected surge in February, reverting to a trend of lackluster performance more in line with modest economic growth, according to Statistics Canada data on Wednesday. Factory sales fell 0.3 percent in March from February to C$49.5 billion ($48.5 billion), below market estimates of a 0.6 percent gain and dragged down by lower prices for energy products and a slump in fertilizer sales. The setback came after sales jumped 2.8 percent in February, the biggest gain since July 2011. Statscan revised the February estimate from 2.6 percent initially. With Wednesday's report, Statscan revised its estimates of manufacturing sales, inventories and orders back to January 2007 for seasonally adjusted data and to January 2009 for unadjusted data to reflect an updated survey sample and other changes. In volume terms, March factory sales increased 0.2 percent. New orders fell by 2.2 percent due mainly to a decline in demand from the transportation equipment industry. Unfilled orders slid 1.1 percent after four months of gains. Statscan said unfilled orders of aerospace products and parts fell because an appreciation of the Canadian dollar in the month affected prices of orders held in U.S. dollars. Inventories edged down by 0.1 percent, but the inventory-to-sales ratio was unchanged at 1.39.