By Roberta Rampton and David Morgan

U.S. President Donald Trump was to make a final push on Thursday to get the support needed to begin dismantling Obamacare in the House of Representatives but faced signs that enough Republicans might oppose the bill to jeopardize one of his top legislative priorities.

The effort is seen by financial markets as a crucial test of Trump's ability to deliver on his legislative agenda, including planned tax cuts. Republican leaders hoped to vote on the health care bill on Thursday, the seventh anniversary of former Democratic President Barack Obama signing his healthcare law. There were indications the House vote could be delayed.

Although Republicans have a majority in the House, Democrats are united against the bill and Trump and House Speaker Paul Ryan, who has championed the bill, can afford to lose only 21 Republican votes. On Thursday morning, MSNBC said a count by NBC News showed that 30 Republicans were planning to vote "no" or leaning that way.

Representative Bradley Byrne, who helps track Republican votes, said he believed Republicans had the support needed to approve the bill but that the chances of passage "get a lot lower if we don't do it this week."

Trump was meeting at the White House with some of the bill's strongest opponents - members of the conservative House Freedom Caucus who say it does not go far enough to undo Obamacare.

"We're still open for negotiations," Representative Ted Yoho, a member of the group, told CNN. "There is still time."

A senior Republican in the House, Ways and Means Committee Chairman Kevin Brady, said Republicans were getting closer to a measure they could agree on.

"I don't know the timing on this but I know we are getting very close," Brady said on Fox News. "I know we still have work to do to make sure members' concerns are heard."

Trump urged Americans in a tweet early on Thursday to press their representatives to vote for the bill, known formally as the American Health Care Act.

Uncertainty over the bill has rattled financial markets and a failure just two months into Trump's presidency would be a setback for the White House, which as late as Wednesday said there was "no Plan B" for the health care measure.

U.S. stock markets have risen steadily in recent months on optimism over a pro-business Trump agenda, but fell back sharply on Tuesday as investors worried that failure to push through the health care bill could have a knock-on effect on other Trump priorities such as tax cuts and infrastructure spending. Wall Street was little changed in early trading on Thursday.

"Investors are concerned ... if this vote goes poorly, then what are the implications for tax reform and repatriation of offshore capital," said John Traynor, chief investment officer at People's United Bank in Bridgeport, Connecticut.

VOTE TIMING
The House vote had been expected by about 7 p.m. (2300 GMT). But by midnight on Wednesday, lawmakers had not yet settled on the timing as conservative and moderate Republicans split on whether there should be additional changes to the proposal.

House Rules Committee Chairman Pete Sessions said the vote could happen as early as Thursday or as late as Monday.

The normally well-scripted House, which runs on tight rules that lay out the duration of debates on legislation and approximate times for votes, was anything but scripted on Thursday.

The Rules Committee, which is the gatekeeper for all legislation heading to the House floor, had not yet set the parameters of the debate, including any amendments that would be allowed. Republicans still did not know exactly what would be in the legislation as they negotiated with undecided colleagues.

With Republicans in control of the White House, the Senate and the House, the party has a chance to achieve what it has aimed to do for seven years - overturn Obama's 2010 Affordable Care Act.

The law aimed to boost the number of Americans with health insurance through mandates on individuals and employers, and income-based subsidies. Some 20 million Americans gained insurance coverage through the law.

The House replacement plan would rescind the taxes created by Obamacare, repeal a penalty against people who do not buy coverage, slash funding for the Medicaid program for the poor and disabled, and modify tax subsidies that help individuals buy plans.

While conservative Republicans are pushing for more aggressive cuts to Obamacare mandates, some moderates in the party are worried that the legislation would hit some of their core voters by depriving them of insurance.

This means changes to the bill to satisfy conservatives would carry the risk of turning moderates against it, and also of complicating the work of their colleagues in the Senate.

The nonpartisan Congressional Budget Office estimated 14 million people would lose medical coverage under the Republican plan by next year. It also said 24 million fewer people would be insured by 2026.

Representative Charlie Dent, a leader of the "Tuesday Group" of House Republican moderates who has said he cannot support the bill, said he believed Republican leaders had not yet corralled enough support to pass the bill.

"I never quite understood the mad rush,” Dent told MSNBC.

The White House sought to convey optimism.

“We are moving full steam ahead," said White House spokeswoman Sarah Sanders. "President and his team talking to members letting them know this is the bill to repeal and replace Obamacare and today is the day to get it done. Looking forward to a good meeting at 11:30.”


(Additional reporting by Susan Cornwell, Jeff Mason, Doina Chiacu, Steve Holland and Richard Cowan; Writing by Frances Kerry; Editing by Michael Perry and Bill Trott)