The Senate this week opens debate a long-awaited, bipartisan immigration reform bill that pairs tighter border security with a 13-year path to citizenship for the nation's estimated 11 million illegal immigrants.

But even as senators inch toward a vote on a sprawling bill that also includes E-Verify requirements for employers and more visas for skilled and nonskilled workers, the prospects for passing such a comprehensive package in Congress grows dimmer by the day.

The chief obstacle the bill faces remains the Republican-led House, where key lawmakers are preparing to tackle immigration reform in a series of more limited bills that don't include a centerpiece of the Senate version, a pathway to citizenship for current illegal immigrants.

"Taking individual bills and packaging them will yield a better result," said Rep. Lamar Smith, R-Texas, a senior member of the House Judiciary Committee.

Senate Majority Leader Harry Reid, D-Nev., is pushing lawmakers to pass the reforms by the July 4 recess, but even if they succeed they face a lengthy, contentious negotiation process with the House.

"There is not a majority in the House to support anything like the Senate bill," Judiciary Committee Chairman Bob Goodlatte, R-Va., said Friday on the Laura Ingraham radio program.

Goodlatte's panel has been considering bills that increase visas for high-skilled workers and require an E-Verify system for employers to ensure they don't hire illegal immigrants. He introduced another bill last week that covers visa security and authorizes state and local governments to enforce federal immigration laws.

"We are going to do this in the House based upon what a conservative immigration reform should be," Goodlatte said.

A bipartisan group of House members is crafting a comprehensive bill similar to the Senate's, including a pathway to citizenship, but that measure has to go through Goodlatte's committee, which is likely to reject it.

The bipartisan group suffered a setback last week when Rep. Raul Labrador, R-Idaho, quit in a dispute over whether newly legalized immigrants should be allowed to receive medical benefits under President Obama's new health care reforms. But the group did pick up critical support from House Budget Committee Chairman Paul Ryan, R-Wis., who could help sway conservatives to embrace the comprehensive measure.

If House negotiators agree to change the comprehensive bill to make it more attractive to Republicans -- chiefly by strenghtening border security, stripping health care coverage or eliminating the path to citizenship from the measure -- they risk losing Democratic votes.

"I think it might get to a tipping point, where the expense is too much in terms of giving up things," said Rep. Raul Grijalva, D-Ariz., a leading member of the House Progressive Caucus, a major voting bloc.

Grijalva said House Democrats are pinning their hopes on the Senate bill becoming the vehicle for a final House-Senate compromise.

"Whatever comes out of the House is not even going to approach the Senate bill, in terms of compromise," said Grijalva.