WASHINGTON (Reuters) - Immigrants for years have paid far more into Medicare's coffers than they have pulled out, effectively subsidizing rising healthcare payments to the aging U.S. population, a study released on Wednesday showed. The analysis from Harvard Medical School showed immigrants generated a $13.8 billion surplus for the U.S. government healthcare program for the elderly in 2009, the most recent figures available. From 2002 through 2009 immigrants posted a Medicare surplus of $115 billion, while the American-born population logged a deficit of $28 billion in contributions. The Harvard study was posted in the June issue of the medical journal "Health Affairs." It counters impressions that immigrants put a strain on healthcare resources.