The plan needs at least 60 votes of support to survive a threatened GOP filibuster. With Heller and 55 members of the Senate Democratic caucus, supporters still need at least four votes. But many GOP senators say they will not back extending the program, because Reed and Heller did not outline a way to pay for the billions of dollars in benefits. And even if the proposal passed the Senate, House Republican leaders have expressed no interest in extending the program because the Senate proposal lacks a "pay for."

Reed argued in an interview that the short-term extension would not require supplemental cuts because Congress historically has considered unemployment benefits as emergency funding.

"Let's get the benefits going for people who need it in difficult times, and then in that three-month period, there's a chance for [lawmakers] to look at longer-term extensions" and find ways to offset the costs of the program, he said in the interview late last week.

During a conference call with reporters Sunday, Reed said he is talking to "everyone" about supporting the extension. But Democratic aides said most of the attention is focused on Republican senators whose states are suffering from high unemployment rates: Sens. Lamar Alexander (Tenn.), Saxby Chambliss (Ga.), Bob Corker, (Tenn.), Johnny Isakson (Ga.), Mark Kirk (Ill.), John McCain (Ariz.), Rob Portman (Ohio), Patrick Toomey (Pa.) and Roger Wicker (Miss.).

Kirk said via Twitter Monday that he would vote against the plan because it "should be offset with spending reductions." Spokespeople for Alexander, Chambliss, Isakson, Portman and Wicker said that the senators would reject the proposal for similar reasons. Aides to Corker, McCain and Toomey said the senators hadn't yet decided how to vote.

Democrats are targeting several other GOP senators who have voted in the recent past to end debate on Democratic-backed legislation, a group that often includes Sens. Kelly Ayotte (N.H.), Susan Collins (Maine) and Lisa Murkowski (Alaska). Aides to those senators didn't respond to requests for comment.

The unemployment insurance program was first expanded during George W. Bush's administration with broad bipartisan support when the nation's unemployment rate hovered around 5 percent.

Reed is a longtime champion of continuing the program and the partnership between a New England liberal and a western conservative is unusual in the sharply divided Senate. But Rhode Island and Nevada are experiencing the highest unemployment rates in the nation, about 9 percent. Eager to herald the partnership, President Obama called Reed and Heller during his Christmas vacation in Hawaii to thank them for their work.

In an interview late last week, Reed expressed optimism that the benefits would eventually be provided.

"My colleagues will recognize that they have many constituents like this also and that this is an important thing to do for them," he said, adding later, "This shouldn't be a Republican or Democratic issue; it's an issue of what do we do for people who are in a tough job market and what do we do overall."

Heller's support is understandable, given his state's unemployment rate, but his decision to co-sponsor the bill is notable, given that he has rarely sided with Democrats on closely watched legislation. Reid heaped praise on his Nevada colleague Sunday.

"Dean Heller is not some maverick that is out spewing socialism," he told CBS's "Face The Nation." "Here's a guy who is really a conservative person, and he wants to extend unemployment benefits. I admire him for doing that. And can't we get four Republicans to agree with the American people that we should do that? I would certainly hope so."