WASHINGTON — Roughly half the nation’s business economists say they think the U.S. economy will slip into recession by the end of next year, and three-fourths envision such a downturn beginning by the end of 2021.The finding comes from the latest survey by the National Association for Business Economics of its member economists. Just 10 per cent of them say they foresee a recession beginning this year. At the other extreme, only 11 per cent expect the economy to avoid a recession through 2021.The economy began its expansion in June 2009, when the Great Recession officially ended. If it endures beyond June this year, the expansion will become the longest on record. Compared with others, the current one has been tepid, with annual economic growth averaging just slightly above 2 per cent.Martin Crutsinger, The Associated Press