The landmark healthcare reform bill, proposed by President Barrack Obama since he came into office, is moving toward the finish line in the U.S. Senate with a crucial test vote in the wee hours of Monday and a final vote later in the week.

However, sharp differences between the Senate's and the House's versions of the bill, lack of solid public support, and some unsolved thorny issues still hinder the bill from forging into a legislation.

Not a done deal

As the last holdout among Democrats on the healthcare reform bill, Senator Ben Nelson (D-Nebraska) agreed on Saturday to support the bill in return for compromise with regard to language in the bill prohibiting federal fundings of abortion and injecting more financial aid to his state.

After securing support from all 60 members of the Democratic caucus in the Senate, Nevada Senator Harry Reid, Majority Leader of the Senate, has been pushed to set a Christmas deadline for final vote on the bill.

Under congressional rules, the passage of the bill needs three separate votes. The first and make-or-break vote was scheduled on 1:00 a.m. Monday (0600 GMT), which aimed to conclude the Republican's long-standing procedural delays on the 871-billion-dollar overhaul.

However, analysts noted that Senate's backup will not mean a done deal, since the bill has to be reconciled with a version passed by the U.S. House and signed by President Obama.

The version-reconciliation task will be up to a conference committee, which is expected to be dominated by senior lawmakers from both chambers close to Senate Majority Leader Harry Reid, D-Nevada, and House Speaker Nancy Pelosi, D-Calif.

Both the Senate and the House then would have to approve a final version before it goes to President Obama to be signed into law.

Obama had expected to sign the historical healthcare legislation in more than four decades by this year end, but his senior advisers acknowledged that it might not happen.

"We're going to have some work to do when we come back from the Christmas-New Year break" David Axelrod, Obama's strategic advisor, told NBC's "Meet the Press" Sunday.

Sharp divisions

Obviously, another crucial step for the healthcare bill ahead will be how fast the Senate and the House can iron out their differences.

In general terms and broad guidelines, the two chambers' versions of the legislation are identical. Both would greatly expand health insurance coverage and bar insurers from denying coverage because of preexisting conditions and coverage.

Meanwhile, both versions support creation of exchanges or marketplaces for insurance policies and both claim that the legislation will cut deficits over the next decades.

However, there are marked differences between the two versions which are difficult to reconcile.

First is the tax issue. The Senate bill raises money by increasing the Medicare tax by 0.9 percentage points from current 1.45 percent on individuals with wages of more than 200,000 dollars and couples earning over 50,000 dollars.

It also would impose a 40 percent excise tax on most high-end expensive insurance policies.

But many House Democrats see the excise tax as a burden on the middle class, and prefer a 5.4-percent income tax surcharge on individuals with adjusted gross incomes of more than 500,000 dollars and couples making more than 1 million dollars.

The second thorny issue is public health insurance option, or public option in short. The House version suggests a government-run health insurance plan to compete with the private insurance sector.

The public option has been what the White House, Democratic leaders and liberals have all sought, while the Senate version will only allow privately-run plans.

Then comes the issue of the availability of coverage for abortion. There are pro- and anti- Democrats in both chambers and neither sides are satisfied with the present abortion clauses in the two versions.