U.S. think tank's immigration study draws conservative fire By Thomas Ferraro and Richard Cowan WASHINGTON (Reuters) - A leading U.S. think tank headed by former Republican Senator Jim DeMint drew fire from fellow conservatives Monday for concluding that the citizenship proposals in a sweeping immigration reform bill would cost taxpayers trillions. The clash underscored divisions within the Republican Party over bipartisan immigration legislation in the Senate backed by Democratic President Barack Obama. The Heritage Foundation, in a report, warned that a proposed pathway toward U.S. citizenship for 11 million undocumented immigrants would cost $6.3 trillion over the next 50 years. During their lifetimes, these immigrants-turned-citizens would take far more in federal services and benefits than they end up paying in taxes, the foundation said. Conservative critics countered that the Heritage Foundation failed to consider the economic advantages of immigration reform, such as improvements in obtaining needed high- and low-skilled workers, while focusing solely on the costs. "This study is designed to try to scare conservative Republicans into believing that the cost will be so giant that you can't possibly vote for it," former Republican Party Chairman Haley Barbour said in a conference call with reporters. Derrick Morgan, a Heritage vice president, responded in a conference call of his own, saying, "We are a research institution here. We can't necessarily speak to the motivations of other people. "But we very much want the fiscal costs to be part of the debate because it protects the American taxpayer," Morgan said. While supporters of an "earned pathway toward citizenship" argue it would help create order, foes charge it would amount to unwarranted "amnesty" drawing more undocumented immigrants. DeMint, a favorite of the conservative Tea Party movement, served in the Senate from South Carolina for eight years before stepping down in January to head the Heritage Foundation. DeMint said the U.S. immigration system is "broken," and that "amnesty will only make the problem worse." Heritage has assumed a leading role in opposing the Senate bill and its study is expected to be the first of many on it. Coming three days before the Senate Judiciary Committee is scheduled to begin debating the immigration measure, the Heritage Foundation study estimated that legalizing the 11 million would put a severe strain on government programs, from healthcare to education. The Heritage Foundation report was blasted by other conservatives even before it was issued. Holtz-Eakin and Norquist both criticized the Heritage Foundation study. In a memo to fellow Republicans in Congress, Norquist wrote that the study "does not speak for the conservative movement." Following the 2012 elections in which 71 percent of Hispanic-American voters supported Obama, many Republicans began re-examining their opposition to immigration reforms.