House Speaker Paul D. Ryan (R-Wis.) leads a Jan. 5 meeting on Capitol Hill to discuss the House’s plan to repeal and replace Obamacare. (Melina Mara/The Washington Post)

House Republican leaders attempted to quell concerns of a skittish rank and file before a key vote Friday to begin unwinding the Affordable Care Act.

The assurances came after lawmakers across the GOP’s ideological divides sounded anxious notes this week about advancing legislation that would repeal Obamacare without firm plans for its replacement.

“We just want more specifics,” Rep. Mark Meadows (R-N.C.), chairman of the conservative House Freedom Caucus, said Wednesday. “We need to know what we’re going to replace it with.” Meadows said he was personally undecided on his vote Friday and that other caucus members were leaning toward no.

Rep. Charlie Dent (R-Pa.), chairman of the moderate Tuesday Group, said members of that caucus have “serious reservations” about starting the process without replacement plans spelled out. “We’d like to have this conversation prior to the repeal vote,” he said.

Those jitters hint at a rocky road ahead as Republicans start trying to fulfill a long-standing campaign promise. They have forced GOP leaders to reassure lawmakers that they will not move precipitously and open Republicans to charges they threw the health-care system into chaos.

(Jenny Starrs/The Washington Post)

“This will be a thoughtful, step-by-step process,” House Speaker Paul D. Ryan (R-Wis.) said Thursday. “We’re not going to swap one 2,700-page monstrosity for another. . . . We’re going to do this the right way.”

The House is set to vote Friday on a measure that would begin the budget reconciliation process, which ultimately would allow Republicans to repeal Obamacare without securing cooperation from Democrats who have vowed to block any major changes to the law.

GOP leadership aides said they were confident the measure would pass Friday, but the vote could still be close — reflecting significant tactical differences on an issue that Republicans have long touted as a chief priority should their party regain the White House.

House action is expected to come barely 24 hours after Senate passage of the measure. Only one senator, Sen. Rand Paul (R-Ky.), crossed party lines — arguing, in part, that the GOP should put forth an Obamacare replacement first.

Complicating matters is President-elect Donald Trump, who this week made several sweeping statements about the timing and substance of his health-care plans.

Replacement of Obamacare, Trump said at a Wednesday news conference, would happen “essentially simultaneously” as its repeal and would be “far less expensive and far better.” In a New York Times interview published Tuesday, Trump indicated that legislation could come together within weeks.

Trump tweeted praise Thursday for the Senate’s swift action, which could help goad skeptical House Republicans: “Congrats to the Senate for taking the first step to #RepealObamacare- now it’s onto the House!”

But several key lawmakers involved in the process indicated that Trump is pushing an overly ambitious timeline. Democrats took more than a year to pass the ACA and related legislation, and they had a filibuster-proof 60-vote Senate majority for much of that time.

“I guess it depends on how you define ‘simultaneous,’ ” said Rep. Michael C. Burgess (R-Tex.), chairman of the House Energy and Commerce subcommittee on health, when asked Wednesday about Trump’s comments.

Rep. Greg Walden (R-Ore.), chairman of the House Energy and Commerce Committee, said, “There’s a lot of different timelines floating around.”

“I think there’s a lot of energy for getting on with both” repeal and replacement, he said. “The question is, what are the formalities for that? We want to have a due process here, we want to have a transparent process. We want to have a full legislative process.”

Another wild card is Trump’s pick for health and human services secretary, Rep. Tom Price (R-Ga.). Trump suggested Wednesday that Price would play a key role in shaping the Obamacare replacement strategy.

“As soon as our secretary is approved and gets into the office, we’ll be filing a plan,” he said. It was unclear whether he meant a legislative plan, or a plan for repealing or modifying Obamacare-related regulations.

House leaders see Price, the House Budget Committee chairman and an orthopedist, as a reliable partner. But it is unclear how quickly he might be confirmed: The Senate Finance Committee has yet to set confirmation hearings, and Democrats have vowed to undertake a no-holds-barred blitz on Price’s record.

“It’s really important to get Dr. Price in as secretary,” said Rep. Patrick J. Tiberi (R-Ohio), chairman of the House Ways and Means subcommittee on health. “That’s going to be key to working with us, and we obviously know a lot about what he thinks about.”

Ryan said Thursday that he and Trump are “completely in sync” on health care and suggested that more details would be on offer at the yearly congressional Republican retreat, which will be held in Philadelphia the week after Trump’s inauguration. Trump is scheduled to address lawmakers there.

“We’re going to have a full, exhausting conversation at our retreat to go through all of these things,” Ryan said Thursday. “What I think people are beginning to appreciate is, we have lots of tools in front of us. It’s not just a one-and-done-bill kind of a thing. And so that’s what we’ve been walking our members through, are all the options available to us to get this done.”

One of the those tools, he said, is budget reconciliation — a process that will pave the way for Republicans to pass a bill gutting major parts of the ACA, including the system of tax subsidies and penalties that Democrats relied on to increase coverage levels.

GOP leaders are examining closely what elements of a replacement plan can be included in a repeal bill set to be passed under reconciliation.

Senate Finance Committee Chairman Orrin G. Hatch (R-Utah) said Thursday that the repeal measure could include some attempts to empower states to begin making health-care coverage decisions before a replacement bill is complete.

Still, Senate rules dictate that only measures with a discrete budgetary effect are permissible under reconciliation. So while Republicans could claim that the bill repealing Obamacare also contains a blueprint for its replacement, major parts of that replacement plan would need 60 Senate votes — and thus significant Democratic support.

According to multiple GOP sources, Republicans are looking at whether to use reauthorizations of existing programs, such as the Children’s Health Insurance Program, as vehicles for replacement measures. That could give them leverage to secure cooperation from Democrats.

Behind the scenes, Republican leaders are urging lawmakers to look at this week’s votes as mere procedural formalities. But some rank-and-file members remain nervous about voting to start a process they might not be able to stop.

“I told my members, in order to have a meaningful impact . . . you better speak up now,” Dent said.

Kelsey Snell contributed to this report.