Nearly 20 percent of U.S. workers underemployed: poll 4:01am EST By David Morgan WASHINGTON (Reuters) - Nearly 20 percent of the U.S. workforce lacked adequate employment in January and struggled to make ends meet with reduced resources and bleak job prospects, according to a Gallup poll released on Tuesday. In findings that appear to paint a darker employment picture than official U.S. data, Gallup estimated that about 30 million Americans are underemployed, meaning either jobless or able to find only part-time work. Underemployed people spent 36 percent less on household purchases than their fully employed neighbors in January, while six...