Washington ? Key Senate Republicans on Wednesday night offered compromise immigration legislation that seeks to sway conservative holdouts by providing slightly less generous treatment for illegal immigrants than the bill now foundering on the floor.

While it remained unclear whether enough conservatives would support it, the Democrats held their fire as Senate Majority Leader Bill Frist, R-Tenn., unveiled an 11th-hour alternative that still would place millions of illegal immigrants on a path to eventual citizenship. With Democrats solidly united behind the idea of legalization, they could potentially provide the votes necessary to push the GOP compromise to victory.

“It moves the debate forward,” Frist said, though he declined to predict the outcome of the vote now expected Friday.

Senate Democratic leader Harry Reid of Nevada didn’t close the door to his caucus offering its support, saying the deal appears to represent “very minimal change” to the legalization plan approved by the Senate Judiciary Committee and backed by Democrats.

“I’m hopeful it’s something we can support,” Reid said.

Key Republicans have been negotiating frantically behind the scenes in recent days as it became clearer that the Judiciary Committee bill wouldn’t garner enough support when it comes up for a vote. The main stumbling block: some conservatives’ belief that it constitutes amnesty by placing illegal immigrants on a direct course to legal permanent residence and eventual citizenship.

Sen. John Cornyn, R-Texas, who was in that camp, issued a noncommittal statement Wednesday night. “Although I’ve not had an opportunity to read this rather lengthy proposal, I remain adamant that we not repeat the mistakes of the 1986” amnesty, he said.

The GOP compromise would treat illegal immigrants differently based on their length of stay, the concept being to make the process simpler for those who have the deepest roots in U.S. society. Under their plan:

Illegal immigrants who arrived after January 2004 (up to 2 million people) would be offered no path to legal status. Proponents suggest the newcomers would leave as jobs for illegal workers dry up amid tighter workplace enforcement.

Those who can prove – using pay stubs, utility bills or other documents – that they’ve been here more than five years would “earn” legalization by working for six years, paying $2,000 in fines and back taxes, undergoing background checks, and learning English and civics.

The estimated 3 million people here for more than two years but less than five years would face a more circuitous path to legal residence. They would be required to leave the United States within three years, if even for just a day, to apply for a temporary worker visa good for six years. They could then, at the end of their visa, apply for a green card providing for legal permanent residence – though the proposal sets aside only 135,000 green cards for low-skilled workers and thus could mean years waiting in a backlog.