Senate Majority Leader Harry Reid’s (D-Nev.) race to pass a health care bill by Christmas is on hold while the Congressional Budget Office analyzes a compromise proposal that could break an impasse among Democrats over the public insurance option.

Private discussions on additional unresolved aspects of Reid’s $848 billion reform package continued Thursday. But talks on the single-biggest issue blocking Democratic unity and passage of the bill — the divide over the public insurance option — subsided as the Conference waited to hear from CBO on the cost of a potential compromise negotiated by a group of 10 liberal and moderate Senators.

Sen. Mark Pryor (D-Ark.), who led the group of 10 negotiators along with Democratic Conference Vice Chairman Charles Schumer (N.Y.), said Thursday afternoon that he expected the CBO to return with a cost estimate “early next week.— One senior Democratic Senate aide said a CBO score could be available Monday.

“My understanding — it always takes CBO a few days to score something that’s complicated like this, as we know from all the various health bills that have been scored,— Pryor said, adding that the Democratic negotiating group “agreed to as much as we could agree to without having a CBO score.—

The public insurance option in the current health care reform bill calls for the creation of a government-run insurance company, but includes an opt-out clause for states that do not want to participate.

In the face of moderate Democratic and GOP naysayers, Reid about 10 days ago assigned a group of moderate and liberal Democrats to work out a compromise to the public option. Details of the plan are sketchy, but it appears it could include an expansion of Medicaid, while allowing individuals ages 55 to 64 to buy into Medicare.

Those two provisions could derail the compromise before it gets off the ground, depending on the result of the CBO’s analysis. Snowe said Thursday that the Medicare buy-in is a nonstarter for her; key moderate Democrats also are skeptical. Meanwhile, expanding Medicaid and Medicare are exactly what attracted liberals to the possible deal and made them comfortable with dropping the public insurance option.

However, Senate Finance Chairman Max Baucus (D-Mont.) said the leadership is looking at ways to address this issue. Baucus said legislative language dealing with concerns over the Medicare buy-in could be inserted into the forthcoming manager’s amendment.

“We’re at that stage where we’re seeing if it can be worked out,— Baucus told reporters. “There are ideas. We have ideas — I can’t get into details. We have ideas, we’re listening to concerns.—

With several components of the reform bill yet to be worked out, Democrats are beginning to hedge on whether the package can be approved before Christmas — Christmas Eve is two weeks away. While optimism was high just after Thanksgiving, Democrats are now pegging their chances at “possible,— rather than “likely.—

“I think it’s possible, I do,— Sen. Maria Cantwell (D-Wash.) said. We’ve “got to keep working — really, really hard.—