WASHINGTON — A bipartisan Senate immigration bill would cost the government a net $6.3 trillion over the next 50 years to provide benefits for millions of people now living in the United States illegally, the Heritage Foundation said in a report Monday, setting off a fierce dispute with fellow conservatives who attacked the study as flawed and political.
The Heritage study said immigrants granted new legal status under the bill would eat up more than $9 trillion in health, education, retirement, and other benefits over their lifetime, while contributing only around $3 trillion in taxes.
Republicans and conservative groups who support the bill quickly countered that the study failed to measure broader economic benefits from an immigration overhaul, including a more robust workforce that would boost the gross domestic product.
‘‘The Heritage Foundation document is a political document; it’s not a very serious analysis,’’ said Haley Barbour, former governor of Mississippi and a Republican who is part of a task force with the nonprofit Bipartisan Policy Center that supports the bill. ‘‘This study is designed to try to scare conservative Republicans into thinking the cost here is going to be so gigantic that you can’t possibly be for it.’’
Jim DeMint, former senator and Republican of South Carolina, the Heritage Foundation’s new president, dismissed such criticism.
‘‘It’s clear a number of people in Washington who might benefit from an amnesty, as well as a number of people in Congress, do not want to consider the costs,’’ DeMint said. ‘‘No sensible thinking person could read this study and conclude that over 50 years that it could possibly have a positive economic impact.’’
The brouhaha developed as both sides prepare for the landmark bill to undergo its first tests later this week in the Senate Judiciary Committee, which will begin voting on amendments Thursday.
It underscored the high political stakes for supporters and opponents, as each jockeyed to define the legislation. And it laid bare splits within the Republican Party, where business-oriented leaders such as Barbour and antitax activist Grover Norquist are pushing for immigration reform, while more ideologically focused lawmakers and groups are voicing increasingly loud opposition.
The Heritage report was a reprisal of a study the group released at the height of the last congressional debate on immigration, in 2007, which said the bill being considered then would have cost $2.6 trillion. That figure, too, was disputed, but it carried weight with Republicans and helped lead to the legislation’s eventual defeat in the Senate. This time, supporters of the bill are determined not to let opponents wrest control of the debate. Anticipating Heritage’s release of its new report, bill supporters responded quickly with conference calls and talking points criticizing its methodology and the foundation’s agenda.
The Heritage authors acknowledged their report does not attempt to offer a comprehensive analysis of the entire 844-page immigration bill, which would boost border security, change legal immigration and worker programs, require all employers to check their workers’ legal status, and offer eventual citizenship to the estimated 11 million immigrants living in the country illegally. Instead, the Heritage study focused almost exclusively on the added costs the government would incur in providing benefits to immigrants here illegally once they gain legal status. These include Social Security, Medicare, unemployment insurance, health care, welfare, public education, and services like police and fire protection, highways, and parks.
The study said an average adult now living in the United States illegally would receive $592,000 more in government benefits over a lifetime than he or she would pay in taxes.
‘‘It becomes extraordinarily expensive,’’ the lead author, Robert Rector, said at a news conference near the Capitol.
Costs are higher for this bill than the last one in 2007, Rector said, partly because government spending has grown more generous.
Heritage is not the only conservative voice opposing the bill. A number of lawmakers led by Senator Jeff Sessions, Republican of Alabama, have also been working to defeat it.
Some talk radio hosts, including Mark Levin and Rush Limbaugh, have begun to voice deep unease despite the efforts of the bill’s conservative standard bearer, Senator Marco Rubio, Republican of Florida, to sell the legislation to them and other conservative opinion leaders. Talk radio was instrumental to the bill’s defeat in 2007.
Meanwhile, supporters have assembled a wide and diverse coalition in support of the bill.
Several groups in that coalition criticized the Heritage report’s assertions Monday, including an assumption that most newly legalized immigrants would remain in households that consume more government benefits than they pay in taxes, discounting the possibility that many would become upwardly mobile, move into higher tax brackets, pay more in taxes, and use fewer services.