WASHINGTON - Senate Democrats pushed for a vote on a bipartisan immigration bill after Republicans foundered while trying to rally GOP support for a compromise on what to do about the millions of illegal immigrants now in the country.

Democrats set up a showdown over a proposal that would allow the illegal immigrants to remain in the country and become permanent residents after paying $2,000 fines and back taxes, learning English and working six years.

"Are the Republicans going to stand up for comprehensive immigration reform or not?" Sen. Dick Durbin, D-Ill., asked Tuesday.

Republicans had floated a proposal Monday night and early Tuesday to divide illegal immigrants between those who have been in the country more than five years and those who have not.

Several rank-and-file Republicans objected, and Majority Leader Bill Frist and fellow Republicans spent much of the day trying to find an alternative.

"I don't know that we're going to get a bill," said Sen. Mike DeWine (news, bio, voting record), R-Ohio. "It's tough."

Sen. Harry Reid (news, bio, voting record) of Nevada, the Democratic leader, blocked numerous attempts by Republicans to hold votes Tuesday on selected amendments. "We do not need a compromise. It's in our bill," he said and later set the stage for a test vote on Thursday.

Democrats need 60 votes to overcome objections from conservatives on the immigration bill approved by the Senate Judiciary Committee that is being pushed by Reid.

Durbin acknowledged the votes to cut off debate and force a final vote are not there, but said Democrats had to move because they feared Frist was going to let the clock expire on the bill, in its second week on the floor.

But Republicans blamed Democrats for inaction. "The other side is delaying, postponing, obstructing and not allowing votes on amendments," Frist said.

The House has passed a bill that would shore up border security by putting the military on the border, requiring employer to verify they've hired legal workers and making being in the country illegally a felony.

A strong Senate bill would mean a better bargaining position in conference committee with the House, Durbin said.