In fact, for those who cannot pitch in much of their own income, even a refundable tax credit is not likely to be enough to pay for a health insurance policy, Democrats say. That is one reason the Republican alternative is not likely to cover as many people as the Affordable Care Act.

At the meeting on Wednesday, several Republican senators expressed concern that the tax credit proposed by House leaders would be available even to people with high incomes who did not need federal assistance.

Earlier, Representative Kevin Brady, Republican of Texas and head of the Ways and Means Committee, said the credit would be a way to provide more equity in the tax code by creating a tax break for people who buy insurance on their own, similar to the break already available to people who get insurance through the workplace.

He predicted that Republicans would overcome their divisions.

“Rather than using his speech to divide Republicans,” Mr. Brady said, “it’s really an opportunity for us to sit down and work through what remaining differences there are, and I’m confident we can.”

Mr. Brady and another architect of the House plan, Representative Greg Walden of Oregon, the chairman of the Energy and Commerce Committee, huddled with Republican senators on Wednesday. But lawmakers left the meeting with many unanswered questions and were not ready to endorse the House plan.

The fractures among Republicans have been on display in the past few days. On Monday night, three senators — Mr. Paul, Mike Lee of Utah and Ted Cruz of Texas — posted on Twitter in support of what they called #FullRepeal.