House Speaker Paul D. Ryan (R-Wis.) speaks during a news conference on Capitol Hill on Thursday, March 2, 2017. Ryan laid out an swift timeline at closed-door meeting Thursday to pass a Republican alternative to the Affordable Care Act within three weeks. (EPA/MICHAEL REYNOLDS) (Michael Reynolds/EPA)

Key House committees are set to take up legislation to repeal and begin replacing the Affordable Care Act next week, with Republican leaders intent on overcoming internal GOP debates to quickly deliver on a central campaign promise.

Those intraparty struggles were highlighted Thursday when a Republican senator joined Democrats in calling for more transparency in the legislation’s drafting and suggested that House leaders were keeping details under wraps to sideline conservatives.

“This is being presented as if it were a national secret, as if this were a plot to invade another country,” said Sen. Rand Paul (R-Ky.) as he stood outside a Capitol conference room where members of the House Energy and Commerce Committee met.

But elsewhere Thursday, GOP leaders expressed confidence that they were about to make good on a seven-year-old pledge to undo the ACA.

House Speaker Paul D. Ryan (R-Wis.) laid out a three-week timeline for the passage of health-care legislation in a closed-door Capitol meeting with fellow Republicans Thursday morning, according to numerous attendees.

The first steps involve parallel action next week by the House Ways and Means Committee and the Energy and Commerce Committee, which are handling separate parts of the ACA overhaul. The following week, the House Budget Committee would move to combine the bills into a “reconciliation” package eligible for expedited Senate debate, with votes on the House floor expected the week after that.

“We are united, and we are determined to rescue people from this collapsing health-care law and to keep our promise to the American people,” Ryan told reporters.

Although there is consensus on many elements of the health-care legislation — expanding health savings accounts, giving states more flexibility to spend Medicaid funds and allowing insurance plans to be sold across state lines — major questions remain that have divided Republicans.

The most important involve how to handle the millions of Americans who were added to the Medicaid rolls as part of the ACA, and how to help millions more who are not covered through their employers purchase affordable insurance.

No legislative text has been released by Ryan’s office or by the relevant committees. A weeks-old draft published Friday by Politico sparked a new round of infighting, and senior GOP aides said leaders have been mindful of keeping the debate internal until key questions are resolved.

One part of the legislation, handled by the Energy and Commerce Committee, was made available to Republican members of that panel — but only to be inspected behind closed doors.

Although members and aides called that standard operating practice for a complex and sensitive bill — “This is not an abnormal thing,” said panel member Rep. Chris Collins (R-N.Y.) — several conservatives balked at the secrecy.

“We’ve been told, ‘It’s take it or leave it. This is what you get,’ ” Paul said. “And I think that’s why it’s top secret. Why don’t they want us to see it?”

Democrats, who were lambasted by Republicans for closed-door dealings during the ACA’s passage in 2009 and 2010, piled on. House Minority Whip Steny Hoyer (D-Md.) and senior Energy and Commerce Democrats wandered around the Capitol complex Thursday, with reporters in tow, searching for the closely guarded legislation.

A core group of conservative lawmakers remains in favor of simply re-passing a 2015 ACA repeal bill that rolled back the Obama law’s key provisions over a two-year time frame but did little to replace them with a new system to help people access health care.

Ryan moved to squelch that effort Thursday: According to two people in the room, Ryan told lawmakers that President Trump does not support passing an ACA repeal bill without replacement elements along with it.

However, there were signs that House leaders were taking conservative criticisms seriously.

Several members of the Ways and Means Committee said they were continuing to work through permutations of the legislation concerning tax code provisions that would help individual Americans purchase insurance and offsetting changes that would keep the plan budget-neutral.

“They feel like there are some of these concerns that have been valid,” said Rep. Mark Walker (R-N.C.), chairman of the Republican Study Committee, a caucus of House conservatives. “That concern has been heard to the place where they feel like it’s something that they need to be working on.”

Congressional budget scorekeepers have not finalized their analysis of the House plans, which several members said would continue to change through the weekend.

All indications Thursday were that the plan will offer Americans who are not covered through their employers or though government plans like Medicare and Medicaid a refundable tax credit to purchase insurance — one adjusted only by age, not by income, as the existing ACA tax subsidies are.

Rep. Tom Reed (R-N.Y.), a member of the Ways and Means Committee, said the tax credits were “a cornerstone” and that “the tax credit being advanceable and portable are critical to the success of the package.”

But conservatives remain wary of that course, saying it would enshrine a federal entitlement. “My major concern is that we’re going to repeal Obamacare but replace it with another giant federal program,” said Rep. Dave Brat (R-Va.).

The funding mechanisms also stand to the controversial among Republicans; one could retain the ACA’s “Cadillac tax” on especially generous employer-provided health plans, while another would cap the existing tax exclusion for premiums paid on employer plans — which would amount to de facto tax hike for millions of Americans.

“You’ve got to pay for this somehow,” said Rep. Mike Coffman (R-Colo.). “All Americans will now have deductibility of their premiums, and there’ll be refundable tax credits for people who would be otherwise eligible for Medicaid expansion. Who’s going to pay for it? Those things cost money.”

Kelsey Snell and David Weigel contributed to this report.