Washington — Congress took its first steps toward reversing President Obama’s health-care reforms on Thursday, but Republican leaders are coming under intense pressure from rank-and-file lawmakers to detail exactly how their “repeal and replace” plans will play out before moving any further.

The Senate voted early Thursday morning on a measure that would allow the use of the special budget reconciliation process to pass health-care legislation. That would allow Republicans to act without securing cooperation from Democrats, who have vowed to block major changes to the Affordable Care Act.

The measure is set for a House vote Friday, but lawmakers across the GOP’s ideological divides have sounded anxious notes about moving forward with Obamacare’s repeal without firm plans for its replacement.

“We just want more specifics,” said 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.”

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.

Neither group has taken a binding position against the procedural measure that will be voted for on Friday. But their wariness has forced House GOP leaders to reassure jittery members that they will not move precipitously or in a way that would open Republicans to charges that they threw the health-care system into chaos by repealing without fully replacing Obamacare.

“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.”