A broad bipartisan immigration deal was threatened Tuesday as the Senate prepared to vote on a Republican proposal to make it harder for millions of illegal immigrants to qualify for green cards.

The proposal by Sen. Wayne Allard, R-Colo., would eliminate extra points that illegal immigrants could get toward lawful status for work done while they were in the U.S. illegally, owning a home, or having health insurance. The proposed merit-based system would award the most credit for employment criteria such as education and skill level.

The Senate also planned to consider a bipartisan bid to require employers to recruit U.S. workers before giving a foreign laborer a job under the measure's controversial new temporary worker program.

Showdowns were expected on Democratic efforts to allow more family-based immigration under the bill and more Republican proposals to make the path to legalization for illegal immigrants more burdensome.

Sen. Edward M. Kennedy, D-Mass., an architect of the bill, said he would oppose the family changes despite his sympathy for the efforts.

"I'm going to stay with the agreement," Kennedy said of the so-called "grand bargain" he struck with conservative Sen. Jon Kyl, R-Ariz., and other Republicans and Democrats from across the political spectrum.

That leaves in doubt the fate of a proposal by Sen. Robert Menendez, D-N.J., to allow more than 800,000 people who had applied for permanent legal status by the beginning of the year to get green cards based purely on their family connections — a preference the bill ends for most relatives who got in line after May 2005.

A close vote was also expected on a bid by Sen. John Cornyn, R-Texas, to bar illegal immigrants who have defied deportation orders from gaining legal status. That could cut down substantially on the number of unlawful immigrants who would be able to take advantage of the measure's path to legalization.

The bill, a top domestic priority for President Bush that poses a perplexing political dilemma for Republicans and Democrats, is widely regarded as the best chance for Congress to take action on immigration — possibly for years to come.

"There are a number of threats and opportunities before us," said Frank Sharry of the National Immigration Forum, part of a coalition of liberal groups pushing hard for passage despite some grave concerns with the measure.

Kennedy said lawmakers who listened to their constituents over a Memorial Day break last week heard that, "the American people want action on immigration reform."

"We know that we are facing some challenges," Kennedy said, referring to a host of amendments that could scuttle the deal.

"Those of us, the dozen or so, who have put this bill together are finding it very, very hot to handle," said Sen. Arlen Specter, R-Pa.

Specter said he'd like to support some of the changes being put forth this week, "but if we're to keep this bill intact to the extent of being able to pass it, there are going to be a lot of very tough votes."

In addition to Menendez's proposal, several Democratic presidential hopefuls have proposed family-related changes.

Sen. Hillary Rodham Clinton, D-N.Y., is proposing allowing more spouses and minor children of legal permanent residents to immigrate to the U.S., by exempting them from visa caps.

The Senate also is considering a bid by Sen. Christopher Dodd, D-Conn., to more than double, to 90,000 a year, the number of green cards available for parents of U.S. citizens.

Sen. Barack Obama, D-Ill., plans an attempt to phase out the point system that gives little credit for family ties to a U.S. citizen or permanent legal resident.