The U.S. Senate passed a sweeping healthcare overhaul on Thursday as expected, which must be combined with a version approved last month by the House of Representatives and passed again by both chambers.

The negotiating conference, which is expected to begin in January, could be difficult given the range of differences, big and small, between the two bills.

But three big issues -- a government-run insurance option, language related to restrictions on federal funds for abortion, and different tax approaches to raise revenue for the changes -- are likely to dominate the negotiations.

Plenty of other smaller details remain to be worked out as well. Here is a look at the biggest sticking points:

GOVERNMENT-RUN INSURANCE OPTION

The House bill includes a government-run public insurance option to compete with private insurers on new state exchanges where the uninsured can compare and shop for coverage. The Senate bill will no longer include a public option, which was dropped to appease moderate Democratic opponents.

House liberals say they will push to reinstate the option in the combined bill, but moderate senators such as Democrat Ben Nelson and independent Joe Lieberman have said they will vote against any bill that includes the proposal.

With Democrats needing every one of their 60 votes to muscle the bill through the Senate, it seems unlikely it will be in a final bill signed by President Barack Obama.

ABORTION

Both the Senate and House bills include compromise language designed to ensure federal funds are not used to pay for coverage of abortions.

The House bill is more restrictive, barring any federal subsidies for plans that cover abortion purchased on the state insurance exchanges and requiring anyone seeking coverage for elective abortions to purchase separate insurance riders.

The Senate plan, negotiated by Nelson, would let states opt out of including plans with abortion coverage on exchanges and require those with abortion coverage to write separate premium checks -- one for abortion coverage and one for the rest.

The House plan was praised by opponents of abortion rights and condemned by supporters. The Senate plan has been condemned by both sides.

Nelson says he will not support a merged bill that changes his abortion language.

In the House, where the healthcare legislation passed with only two votes to spare, about a dozen members backed the bill only after the abortion language was added. If even a few of these defected, it could threaten final passage.

TAX REVENUES

While not gaining as much attention as the public option and abortion, this could be the thorniest topic of all.

The House and Senate rely on different approaches to help raise the money to pay for the bill. The House has a tax on the wealthiest Americans, while the Senate taxes expensive insurance plans -- and large blocs in each chamber have flatly declared their opposition to the competing approach.

The Senate bill also raises payroll taxes on the wealthiest Americans for Medicare, the government health program for the elderly.

A FEW OTHER ISSUES

Both the Senate and the House require most individuals to obtain health insurance, but have different penalties for those who fail to get coverage. The Senate bill allows those up to age 26 to stay on parents' policies, while the House bill would allow dependent coverage up to age 27.

The House bill requires employers with payrolls above $750,000 to provide health insurance to workers. The Senate bill has no employer mandate. But firms with more than 50 workers would have to pay a fine of $750 annually per worker if any of their employees obtain federally subsidized coverage on the exchange.

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