Max Baucus, the centrist Democratic senator, got a boost from the non-partisan Congressional Budget Office on Wednesday night when it estimated his healthcare reform plan would cost $829bn over the next decade – well within the Obama administration’s upper ceiling.

The release of the CBO estimates, which also projects that the bill would reduce the overall fiscal deficit by $81bn over the next decade, means the focus now switches to the critical vote of the Senate finance committee.

Once it passes out of committee, the bill would move to its end-game stage on the Senate floor after having been merged with the more liberal version passed by the Senate health committee earlier this year. Harry Reid, the Senate majority leader, is expected to take about a week to merge the two versions.

But there is still uncertainty over how long Mr Baucus will take to pass it out of his committee. “Right now no-one is sure whether Senator Baucus has the votes to pass it,” said a staff member for another Democratic senator. “Obviously, he won’t push it to a vote until he is sure it will pass.”

A spokesman for Mr Baucus said he had not yet decided when to schedule a vote. The uncertainty revolves principally around four senators in a committee that splits 13-10 between Democrats and Republicans. Of the Republicans, only one, Olympia Snowe of Maine, is considering a possible vote in favour of the bill. Her vote would be symbolically important to the White House, which has long pushed for bipartisan support.

More troublesome for Mr Baucus, who has come under strong fire from the left for jettisoning the “public option”, or government insurance plan, in favour of a more diluted system of public cooperatives, are the still-undecided votes of Jay Rockefeller and Ron Wyden, more liberal Democratic senators from West Virginia and Oregon, respectively.

Mr Rockefeller tried and failed to get the bill amended to include the public option. Mr Wyden is thought to be upset that his alternative healthcare reform bill received scant consideration from Mr Baucus. In addition, there is uncertainty whether Ben Nelson, the centrist Democrat from Nebraska, would support a bill that administers cuts to providers of Medicare, the healthcare programme for US retirees.

On Wednesday, Mr Baucus trumpeted the CBO numbers, which also project that it would reduce the overall US fiscal deficit by between a quarter and a half a percentage point of gross domestic product in its second decade. “Health reform should be fiscally responsible as it expands and improves coverage and these [CBO] numbers reiterate that real reform can be just that,” said Mr Baucus.

Robert Blendon, a professor at Harvard University and the nation’s leading healthcare pollster, said it was very hard to predict where public opinion would settle on the emerging Senate plan. “Just because the bill is centrist doesn’t mean it will be popular,” he said. “Families will be looking very closely to see how it specifically affects each of them.”