UPDATE 1-SCENARIOS-US Senate now in healthcare spotlight

(Adds second Republican backing health reform, details)

By John Whitesides

WASHINGTON, Nov 7 (Reuters) - After a narrow win in the U.S. House of Representatives, President Barack Obama's fight for a sweeping healthcare overhaul moves to the U.S. Senate where it faces a difficult path to approval.

The Senate's version of healthcare reform has been stalled as Democratic leader Harry Reid awaits cost estimates from congressional budget analysts and searches for an approach that can win the 60 votes needed to overcome Republican procedural hurdles.

Eventually, the House and Senate will have to reconcile their separate bills into a single proposal that can be signed by Obama, who has set a now-threatened goal of finishing work by the end of the year.

Here is a look at how the issue might play out as it moves through Congress over the next few weeks:

SENATE BILL

Reid has made his toughest decision in merging the separate bills passed by the Finance and Health panels: He included a national government-run public insurance option, which was part of the Health bill but was not in the Finance measure.

Reid also included a compromise that would allow states to decline to participate, or "opt out," of the government-run program -- an effort to appease moderates, most from conservative Republican-leaning states, who oppose a national public option.