(Adds details on Trump statement, comment from Senate aide, background)
WASHINGTON, July 24 (Reuters) - A seven-year Republican effort to repeal and replace Obamacare faces a major test this week in the U.S. Senate, where lawmakers will decide whether to move forward and vote on a bill whose details and prospects are uncertain.
The Senate will decide as early as Tuesday whether to begin debating a healthcare bill. But it remained unclear which version of the bill the senators would ultimately vote as lawmakers prepared to hear from U.S. President Donald Trump later on Monday.
Trump last week initially suggested he was fine with letting former President Barack Obama's signature law collapse before later urging Republican senators to hash out a deal.
The Republican president is scheduled to make a statement on healthcare at 3:15 p.m. (1915 GMT) following a meeting with people the White House said were harmed by the Affordable Care Act.
"Republicans have a last chance to do the right thing on Repeal & Replace after years of talking & campaigning on it," Trump tweeted on Monday.
Republicans view the 2010 health law, also known as Obamacare, as a government intrusion in the healthcare market. They face pressure to make good on campaign promises to dismantle it.
But the party is divided between moderates, concerned that the Senate bill would eliminate insurance for millions of low-income Americans, and conservatives who want to see even deeper cuts to Obama's framework.
The House in May passed its healthcare bill. Senate Republicans have considered two versions but have been unable to reach consensus after estimates showed they could lead to as many as 22 million fewer Americans being insured. A plan to repeal Obamacare without replacing it also ran aground.
A Senate Republican aide on Monday said the Senate will vote this week on whether to begin debate on the House-passed healthcare bill. If that procedural vote succeeds, the House bill would then be open for amendment on the Senate floor.
If the Senate approves a motion to begin debating a healthcare bill, Majority Leader Mitch McConnell will determine which proposal has the most Republican support and move forward to a vote, Republicans said.
Republicans hold 52 of 100 Senate seats. McConnell can only afford to lose two Republican votes as Democrats are united in opposition.
Senator John Barrasso, a member of the Republican leadership, acknowledged on Sunday that there remained a lack of consensus among Republicans.
"Lots of members have different ideas on how it should be best amended to replace what is really a failing Obama healthcare plan," Barrasso said on CBS's "Face the Nation."
The Republican effort has also been complicated by the absence of Senator John McCain, who has been diagnosed with brain cancer and is in his home state of Arizona weighing treatment options.
Uncertainty over the healthcare's future has left health insurance companies and U.S. states as well as hospitals and other doctors unclear about future funding and coverage.
Public opinion polls also show Americans worried about potential changes to the healthcare system.
(Reporting By Amanda Becker; Additional reporting by Susan Heavey; Editing by Caren Bohan and Nick Zieminski)