Republicans opposed to citizenship for illegal immigrants on Wednesday killed White House hopes that a major reform bill seen as key to President Barack Obama's legacy could soon land on his desk.
The administration meanwhile lashed out at Republicans in the House of Representatives, warning they should not kill the reform drive just to appease "far right" conservative rivals who are after their jobs.
The comprehensive immigration reform bill, which provides a path to citizenship for 11 million undocumented immigrants and strengthens security on the US-Mexico border, has already passed the Senate.
But there are growing fears among reform advocates that the drive will wither and die in the Republican-led House.
Following a crunch meeting of the Republican caucus, House leaders said they would let the Senate bill languish and that the best the White House could hope for is a set of piecemeal measures.
Speaker John Boehner and House Majority leader Eric Cantor in a joint statement pledged a "step-by-step" approach to fixing a "broken" immigration system.
They argued that Americans were "alarmed by the president's ongoing insistence on enacting a single, massive, Obamacare-like bill (referring to the president's health care reforms) rather than pursuing a step-by-step, common-sense approach."
Earlier, White House spokesman Jay Carney acknowledged that passing the bill was "an uphill battle."
"It cannot be acceptable broadly and in the long term that immigration reform would be blocked because some minority of House Republicans is concerned about a primary challenge from the far right," Carney said.
But Republicans emerged from the House meeting insisting that they would not speed through legislation.
"We don't want to rush anything, we want to get it right," said Paul Ryan, the 2012 Republican vice presidential nominee.
Some conservatives were adamant that there not be a pathway to citizenship for all 11 million undocumented immigrants, saying it would merely reward people who broke US laws.
"An accelerated or preferential treatment leading to citizenship is something that I see resistance (to) among House Republicans," said congressman Doug Lamborn.
He added that there is "uniform agreement that border security has to come first, or we're going to end up in this situation again at some point in the future."
National Republican leaders recognize that scuppering immigration reform could be politically disastrous, given the issue's importance to the increasingly powerful Hispanic voting bloc.
But many House Republicans, with few Hispanics in their districts, have little incentive to back a bill fiercely condemned as "amnesty" by many conservatives.
The White House, which stayed in the background for much of the Senate debate on immigration reform last month, is trying to crank up the pressure on House Republicans to force them to pass the bill.
In a report issued on Wednesday, the administration argued that the bill would grow the economy by 5.4 percent and cut federal deficits by nearly $850 billion, while the federal debt would drop three percent as a share of the economy by 2023.
House Republican Jeff Fortenberry insisted he was feeling no heat.
"The Senate does not tell the House what to do," he said.
Adding to pessimism about the bill's chances, Boehner has made clear he will not try to build a coalition to pass the legislation among more moderate Republicans and minority Democrats.
Such a move could lead to a bill's passage, but could also fatally weaken Boehner's power base among restive Republicans.
The standoff will pit House Republicans against influential members of their party in the Senate, including Marco Rubio, who was instrumental in framing the bill and is a possible 2016 presidential candidate.
Democrats meanwhile touted recent polls showing that a majority of voters in some key districts back the Senate legislation and that Republicans who oppose it could be hurt in mid-term elections in 2014.
Public Policy Polling director Tom Jensen said that surveys of seven congressional districts with Republican incumbents and a history of close elections showed that "voters are just much less likely to vote for somebody if they vote against immigration reform."
Brad Woodhouse, president of pro-Obama grassroots group Americans United for Change, was more blunt.
"Their majority is in jeopardy if they screw this up," he said of the challenge facing Republicans.
"There may be nothing more convincing to Republicans who have repeatedly opposed immigration reform in the past... than the political price they'll pay if they fail to pass immigration reform now."
Republican lawmakers largely dismissed that suggestion.
"We want to fix this problem and fix it for good, and not be concerned about political outcomes," said congressman John Fleming, who insisted there is "no panic, there's no rush" about getting a bill done this summer.