G.O.P. Opponents Plan Attack on Immigration Bill Charles Dharapak/Associated Press Senator Jeff Sessions of Alabama is among Republicans planning to use amendments as a way to slow down an immigration bill. WASHINGTON - Republican opponents of legislation to overhaul the nation's immigration laws are readying an offensive intended to hijack the newly released bill as the Senate Judiciary Committee on Thursday begins a review that will offer the clearest sign yet of how difficult a path the legislation faces. With the committee expected to spend at least three weeks on the legislation, Republican critics could offer hundreds of amendments to try to reshape the overhaul. They include proposals that could lengthen the timeline for a pathway to citizenship and that could tamper with an already fragile deal negotiated between business and labor groups for a guest worker program. Anticipating an onslaught, Democrats are preparing a robust defense in an effort to keep the legislation largely intact. For the bipartisan group of eight senators who drafted the legislation and now hope to shepherd it through committee and onto the floor, each amendment is a potential hurdle. "They'll be looking to throw obstacles in the way of the process and propose poison pills in order to frame the debate for the far right," said Frank Sharry, the executive director of America's Voice, a pro-immigration group, referring to some of the potential Republican amendments. What they're really doing is playing towards conservatives, trying to make Marco Rubio and other Republicans uncomfortable, and mobilizing grass-roots opposition. Senator Jeff Sessions, Republican of Alabama and a member of the committee, has long been a vocal opponent of the immigration overhaul, and he signaled last week that he planned to try to slow down the legislation's progress by offering amendments that would "confront the fundamentals of the bill." "The longer this legislation is available for public review, the worse it's going to be perceived," Mr. Sessions said Monday in a phone interview. The longer it lays out there, the worse it's going to smell. The tide is going to turn. The committee will take up the legislation just days after the Heritage Foundation released a report that estimated that the measure, which would offer a path to citizenship for the 11 million undocumented people already in the country, could cost taxpayers at least $6.3 trillion over time. Though the foundation's analysis, issued Monday, has come under scrutiny and criticism, a similar report helped kill an immigration overhaul effort in 2007, and many Democrats on the committee expect the Heritage study to come up. Mr. Rubio, a Florida Republican and a particularly high-profile member of the bipartisan group, is not on the committee but plans to work with his colleagues to shape the bill from the outside. "We're working with other senators on the Judiciary Committee to improve the border security triggers, limit the discretionary power given to the administration and address concerns to make sure that today's illegal immigrants are not eligible for federal benefits," Mr. Rubio said in an e-mail statement. It's clear that if the bill isn't improved, it won't ever become law. Four of the bipartisan group's members sit on the Judiciary Committee - Democrats Richard J. Durbin of Illinois and Charles E. Schumer of New York and Republicans Jeff Flake of Arizona and Lindsey Graham of South Carolina - and immigration advocates are looking to them to protect the bill. Members of the group have generally agreed to band together to vote down all amendments that they believe would undermine the core of the original bill. "The Judiciary Committee is going to be a good proving ground for our bill because the committee includes some of the Republican Party's most vocal opponents of immigration reform," Mr. Schumer said. By honing our responses to their criticisms, and perhaps even accepting some suggestions for improvement, our compromise will be all the more battle-tested when it hits the floor. While the group intends to try to beat back both Republican and Democratic amendments, its members want to do whatever they can to broaden bipartisan backing. Not only do group members want a strong vote out of committee, but they are also aiming for broad support for the legislation in the Senate - 70 votes, by some estimates - to help gather the momentum needed to push the bill through the Republican-controlled House and onto President Obama's desk. "I don't think that all the Republican amendments will be shot down," said Marielena Hincapié, the executive director of the National Immigration Law Center, an advocacy group for low-income immigrants. I think the gang members on the committee really know they want to come out of this with a bipartisan product, and they know they will have to vote in support of some Republican amendments, even if it does move the bill a little bit to the right, for both political and substantive reasons.