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 U.S. 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 former Mississippi Gov. Haley Barbour, a Republican who’s part of a task force with the nonprofit Bipartisan Policy Center, which 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.”

Former Sen. Jim DeMint, R-S.C., 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 both 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 anti-tax 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.

WASHINGTON – President Barack Obama took his congressional outreach effort to the green on Monday by playing a round of golf with a bipartisan trio of senators, including one who sank a hole-in-one.

The pressure of playing with a president who rarely invites lawmakers along to golf didn’t seem to intimidate Sen. Saxby Chambliss, R-Ga., who aced the 11th hole. Rounding out the foursome were Sens. Bob Corker, R-Tenn., and Mark Udall, D-Colo.

Obama took the senators to a favorite course at Maryland’s Andrews Air Force Base, where he frequently plays on weekends with aides and friends. He once took along House Speaker John Boehner, R-Ohio, and has also included Rep. Jim Clyburn, D-S.C., but this was his first outing with any lawmaker in his second term.

“We had a delightful day of golf with folks who enjoy playing the game,” Chambliss said in a statement from his office, which disclosed the hole-in-one. “We talked some business, but it was mainly a day for everyone to get away from the office for a little while.”

Under overcast skies, the three chatted casually with Obama, wearing a windbreaker and baseball cap. They putted on the first green before The Associated Press

One line for cutline goes to boPresident Barack Obama, right, with Sen. Bob Corker, R-Tenn., left, on the first hole of the golf course at Andrews Air Force Base, Monday, May 6, 2013.