WASHINGTON — The White House and Republican House leaders came together Friday behind the plan now moving through Congress to overhaul the Affordable Care Act, including a provision criticized by conservatives pressing for a more aggressive attack on the law.

After President Trump met at the White House with key House committee chairmen, his chief spokesman said the president fully supports the bill’s timeline for phasing out the expansion of Medicaid under the ACA, which some on the right would like to accelerate. Earlier in the day, House leaders dismissed the idea of speeding up the phaseout, as they have done for several days.

“Right now, the date that’s in the bill is what the president supports,” White House press secretary Sean Spicer told reporters, adding, “It’s not a question of negotiation.”

Spicer’s comments indicated that Trump has taken the side of GOP leaders in their battle with House conservatives, who have been pressing for a more dramatic rollback of Obamacare for weeks and insist that the pending legislation cannot pass the House without significant changes.

The development also suggested that Trump had reversed himself after meeting with House leaders Friday; earlier in the week, the president told conservative lawmakers and leaders of outside conservative groups that he was open to significant further negotiations.

If so, Trump’s stance gives House Speaker Paul Ryan, R-Wis., the measure’s top booster, new momentum at the end of a difficult week of conflict between conservative members of Congress and GOP leaders.

The chairman of the House Freedom Caucus, the hard-right faction that contains the plan’s most vocal Republican critics, insisted Friday that Trump’s position “has not changed,” citing “continued conversations” with White House budget director Mick Mulvaney.

“He’s willing to get the very best of any deal, and he knows that there is a real willingness to negotiate in good faith to get a better bill,” Rep. Mark Meadows, R-N.C., said.

Both sides have been speaking to Trump, and each has hoped that he will help wear down the other, putting the president at the center of a fierce intraparty clash. Even now, the lack of clear guidance from Trump has left both sides jockeying to argue their case to him last.

Next week, the independent Congressional Budget Office is scheduled to release its estimates of the bill’s cost and impact on insurance coverage, threatening to upend the debate anew.

But Friday, the proxy battle concerned the ACA’s expansion of Medicaid, the federal health-care program for low-income Americans. The American Health Care Act, as the GOP proposal is named, would phase out the expansion by 2020, but conservatives want it to end next year.

House Majority Leader Kevin McCarthy, R-Calif., said at a Friday news conference on Capitol Hill: “I think right now that would be very difficult to do.”

Before meeting with the committee chairs Friday, Trump congratulated them for advancing the legislation in marathon sessions this week and voiced optimism about the road ahead. “This is the time we’re going to get it done,” he said.

The GOP leaders said afterward that they were willing to listen to different perspectives but warned against stalling.

“We’ll continue to listen; we’ll continue to make improvements where we can,” said Rep. Kevin Brady, R-Texas, chairman of the House Ways and Means Committee. “But there’s no question: This is the bill at the end of the day that will come to the president’s desk.”

“We are ready to go, and the worst thing we could do is hit the pause button and continue Obamacare and its broken policies,” said Rep. Greg Walden, R-Ore., chairman of the Energy and Commerce Committee.

And in a Friday radio interview with conservative host Hugh Hewitt, Ryan warned that any deviation from the plan set in motion would be “momentum killing.”

Meadows said Ryan and other party leaders were being unreasonable: “To suggest that they’re willing to listen but that no substantial changes would be made sends a real clear message that ‘we appreciate your input, but we don’t appreciate your amendments.’ ”

Walden said Friday that changing the phaseout date would upset a carefully crafted bill that was negotiated with key parties off Capitol Hill.

“I’ve had discussions all along about different dates, different timelines with governors, with insurance commissioners, with leaders of each of these different groups,” Walden said. “What we want to make sure is that we don’t create a gap. . . . Our best effort is what you see before us.”

Friday’s White House meeting came the day after the House GOP proposal cleared the Ways and Means and the Energy and Commerce committees on party-line votes.

During a Thursday meeting with Trump and Mulvaney, Meadows and fellow Freedom Caucus member Rep. Jim Jordan, R-Ohio, expressed concerns about the House plan, including how it addresses the Medicaid expansion, said a person familiar with the gathering, speaking on the condition of anonymity to reveal details of a private conversation.