The leader of the House of Representatives -- a persuasive arm-twister and deal maker -- faces her toughest challenge yet in the coming weeks: getting 216 votes to pass final legislation revamping the U.S. healthcare system.

House Speaker Nancy Pelosi is scrambling to hit that number and will likely have to rely solely on fellow Democrats, many of them undecided. All Republicans appear lined up against it.

If all Democrats voted as they did last year on an earlier version of the bill, Pelosi would reach 216. But many may switch from yes to no -- or no to yes.

This is her toughest political and legislative battle since becoming speaker in 2007, said Ethan Siegal of The Washington Exchange, a private firm that tracks Congress for institutional investors.

She doesn't have the votes yet, but nobody is counting her out, Siegal said. She's proven that she knows how to get them.

If Pelosi prevails, President Barack Obama will be a big step closer toward signing into law an overhaul of the $2.5 trillion U.S. healthcare system.

But if Pelosi falls short of 216, a simple majority, public anger about the often-gridlocked Congress may mount, making it more difficult for Democrats to retain control of the House in the November election. If Republicans take over, Pelosi's reign as the chamber first woman speaker would end.

Last year, Pelosi won House approval of virtually every item on Obama's agenda, including a $787 billion economic stimulus package, regulatory reform, pay equity for women and an earlier version of healthcare reform.

Another top priority, legislation to curb global warming, appeared to be in trouble in June. But Pelosi lobbied members, one by one, until she got the votes to pass it.

Though much of the House-passed legislation got stalled in the Senate by Republicans and some energy-state Democrats, Pelosi's long list of successes won her praise from outside congressional experts and got her a runner-up spot in Time magazine's annual person of the year.

Pelosi has been as effective as any speaker in modern times, said Norman Ornstein, a congressional scholar at the conservative-leaning American Enterprise Institute.

A lot of people don't like Pelosi, Ornstein said. She gets a lot of flak from her left. But she constantly pushes ahead to make the House do things,

DON'T CROSS PELOSI

Chris Krueger, a congressional analyst at Concept Capitol, said Pelosi is able to effectively work with House Democrats, liberals, conservatives and moderates.

She also raises money like a rock star (for them), commands loyalty and she is tough, Krueger said. People are afraid to cross her.

A Democratic leadership aide said, Pelosi knows members' concerns, she visits their districts, her door is always open to them and she works hard. It's contagious.

Pelosi has a blunt message for Democrats: It will take political courage to vote for the healthcare legislation, but the American people need it.

Polls show that the legislation, denounced by Republicans as a government takeover, is unpopular. But surveys also find that most Americans favor what it seeks to accomplish -- reduced costs, federal regulation of the industry and coverage of tens of millions of uninsured Americans.

House and Senate Democrats passed healthcare bills last year. But efforts to merge the measures and send a final version to Obama collapsed in January when Democrats lost their 60th Senate seat in a special election in Massachusetts that ended their ability to clear Republican procedural roadblocks.

So Democrats regrouped.

They now aim to get the House to approve the Senate version by the end of this month, and then, with a simple majority vote, have the Senate agree to changes to meet House concerns with that bill.

Pelosi voices confidence that Democrats can pass the Senate-approved healthcare bill even though about a dozen abortion rights opponents -- including some who voted for a House bill in November -- say they will oppose it.

Every legislative vote is a heavy lift around here. You assume nothing, Pelosi said. We will pass a bill.

(Editing by David Alexander and Cynthia Osterman)

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