Democratic leaders in the U.S. House of Representatives unveiled a bill on Thursday to reform the U.S. healthcare system, President Barack Obama's main domestic objective.

Senate Democratic leaders are also working on their version of a healthcare overhaul. Here are the likely steps to come as the bill moves through Congress:

* Democratic leaders in the House of Representatives hope to move their 1,990-page healthcare bill to the floor for a one- or two-day debate by late this week. It includes a government-run public insurance option and a new tax on the wealthiest Americans to pay for it.

* House Speaker Nancy Pelosi must put together 218 votes for passage in the 435-member House, where Democrats control 256 seats. She will need to placate liberals in her party who want a stronger version of the public option and about 40 moderate Democrats who want stronger language ensuring that federal funds are not used to pay for abortions.

* In the Senate, Democratic leader Harry Reid is awaiting cost estimates from the Congressional Budget Office on various parts of the legislation. He will use those estimates to help make his final decisions on melding two pending measures and publishing a final Senate healthcare bill. That could happen within the next few weeks.

* Reid already made his biggest decision -- to include a government-run public insurance option backed by Obama and congressional liberals. He added a compromise provision that would let states choose to opt out of participation in the national plan.

* Democratic aides said the Senate bill could drop a mandate that all employers offer insurance to workers or pay a penalty. Differences over the amount of subsidies offered to help lower- and middle-income people buy insurance and the taxes imposed to pay for the plan must also be overcome.

* Reid's goal is to hold the support of liberal Democrats without driving off moderates -- all in hopes of holding together the Democrats' 60-vote majority in the 100-member U.S. Senate. That is the exact number needed to overcome Republican procedural hurdles.

* If the Senate and House each pass a healthcare overhaul, a conference committee composed of members from each chamber will be appointed to negotiate the differences and combine the two measures. The public insurance option is certain to be one of the biggest issues there as well.

* It is at this stage where Obama and White House staffers can become most active in closed-door negotiations, cementing what they want in a final bill and what they think is most likely to pass in each chamber.

* Once the conference committee settles on a single bill, the House and Senate vote again on the revised measure. If approved, it will be sent to Obama for his signature or veto. Obama has set a goal of the end of the year for final action, and congressional leaders hope to finish work for the year by Dec. 18. But the healthcare debate could extend to January if necessary.

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