By John S. McClenahen A 6.1% increase in prices for imported petroleum was primarily responsible for March's 0.9% rise in the U.S. Import Price Index, the U.S. Labor Department reported on April 7. Economists generally expected the index to rise 0.5% last month. Petroleum prices have increased in nine of the last 10 months. Prices for building supplies, unfinished metals and other non-petroleum imports also rose in March, although the 0.2% increase was significantly less than February's 0.4% rise and January's 0.8% increase. On the other side of the trade ledger, the price index for items the U.S. exports to the rest of the world also rose 0.9% in March. A 3.3% rise in prices for soybeans and other agricultural products was responsible for most of the increase. Prices for capital goods and other non-agricultural exports rose 0.6% last month, pretty much the same as in January and February of this year.