WASHINGTON — A week that Senate Republicans had hoped would mobilize conservatives and shore up support for their measure to repeal the Affordable Care Act instead ended with eroding enthusiasm, as usually reliable Republican senators from red states blanched at its impact on rural communities.

With Congress set to return on Monday after a week’s recess, Republican lawmakers are increasingly aware that their seven-year promise to dismantle President Barack Obama’s largest policy achievement is deeply imperiled. Senator John Hoeven, Republican of North Dakota, signaled this week that he would not vote for the bill as written, following negative remarks from other senators with large poor and rural populations. That was the 10th defection.

Three other Republican senators, Bob Corker of Tennessee, Charles E. Grassley of Iowa and John Boozman of Arkansas, have withheld their support, although they have not declared their opposition, and others have largely remained silent.

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Mr. Grassley told voters on Friday that he was unsure if he would vote for the Senate Republican bill in its current form, according to The Des Moines Register. “I don’t even know if we’re going to get a bill up,” said Mr. Grassley, an expert on health policy and taxes who has been in Congress for more than 40 years.

In small counties, rural hospitals and other health care providers are often the largest employers, and after years of railing against Mr. Obama’s law, Republican senators are now grappling with the impact of its possible demise.

“I am a product of rural Kansas,” Senator Jerry Moran, Republican of Kansas, told constituents this week. “I understand the value of a hospital in your community, of a physician in your town, of a pharmacy on Main Street.”

Well short of the 50 votes needed to pass his bill, Senator Mitch McConnell of Kentucky, the majority leader, repeated his fears this week that his party may be stuck tweaking the Affordable Care Act with Democrats. He raised the prospects of a bipartisan fallback last week on the driveway of the White House, and again on Thursday in Glasgow, Ky.

If Republicans cannot pass a bill on their own, they may need to work with Democrats on short-term measures to stabilize insurance markets that, by their account, are on the verge of collapse in many states.

The original Republican opposition to the repeal bill was led mainly by senators from states that have expanded their Medicaid programs under the Affordable Care Act, providing coverage to millions of people who had been uninsured. Now senators from largely rural states, where hospitals stand to lose millions of dollars under the bill, are expressing concerns.

On Thursday, Mr. Moran faced constituents upset at the prospect that the health law might be repealed, and he reiterated his opposition to the bill as it stands now.

Earlier this week, Mr. Hoeven, after a round table with health care executives in North Dakota, said he did “not support the Senate health care bill in its current form.”

Republican leaders may have worried most about Republican senators from states that expanded Medicaid and feared the loss of federal funds, but objections have also come from other places. Twenty Republican senators are from states that have expanded Medicaid; 32 are from states that have not.

Those nonexpansion states are concerned that the repeal bills devised by Republicans in both houses of Congress could harm their residents.

Health care providers and others in the nonexpansion states worry that the legislation would lock in significant disparities in federal Medicaid spending, to the disadvantage of those states.

“We need Medicaid parity,” said Herb B. Kuhn, the president of the Missouri Hospital Association. “Our research shows that per capita federal spending on Medicaid would be much higher in states that have chosen to expand Medicaid, two-thirds higher in 2026. We’d be left with ‘have’ and ‘have-not’ states.”

In Georgia, doctors, hospitals and business groups expressed similar concerns. “Without the increased federal funding that comes with Medicaid expansion, health care providers in nonexpansion states are left with all of the cuts, but none of the coverage,” said a letter to Senator Johnny Isakson, Republican of Georgia, from the Georgia Chamber of Commerce, the Georgia Academy of Family Physicians and the Georgia Hospital Association.

And in a letter to Mr. Moran, Kansas’ health care providers said the Senate bill was “uniformly inequitable to states like Kansas that have not expanded Medicaid.”

The Senate bill would provide some financial assistance to nonexpansion states, estimated by the Congressional Budget Office at $29 billion in the coming decade. But Mr. Kuhn said the funds “fall far short of true equity.”

In Texas, hospitals are putting pressure on Senator Ted Cruz, the state’s junior Republican senator, who is up for re-election next year. If the Senate bill is adopted, said Ted Shaw, the president of the Texas Hospital Association, more people will be uninsured and “more Texans will be forced to rely on hospital emergency departments for care.”

In rural areas where people tend to be older and sicker and have lower incomes, many hospitals say they are already struggling to survive and would be hit hard by the cuts to Medicaid in the repeal bills.

“I talked with the marketing director of the small hospital in Greenville, Maine, yesterday at lunch,” said Senator Susan Collins, Republican of Maine, who has opposed the bill. “She told me that the hospital is the biggest employer in town, with 180 employees, and that it relies on Medicaid for 65 percent of its revenues. It is unlikely that this community hospital could survive the cuts that are in the Senate bill.”

“In addition, if it were to close, the economic blow would be devastating because of the loss of so many good-paying jobs,” she continued. “I am not surprised that those of us who represent rural states that would be particularly hard hit by the Medicaid cuts tend to be particularly concerned” about the impact of the bill.

Republicans are quick to point out that while providers, patient advocacy groups and medical associations have generally opposed the bill, Republicans have avoided making the sorts of deals that the Obama administration cut with hospitals, drug companies, insurance companies and other groups to get its bill passed.

House Republicans are watching the efforts in the Senate with concern. They passed their own bill this spring that has proved unpopular, and they will not be pleased to have taken a difficult vote only to have the Senate punt, perhaps the worst-case situation for them as they prepare to defend their majority next year.

Many shied away from town hall-style meetings during the recess to avoid engaging with voters and protesters on the issue.

“I don’t want to have a situation where we just have a screaming fest, a shouting fest where people are being bused in from out of the district to get on TV because they are yelling at somebody,” said the House speaker, Paul D. Ryan, on Friday in his home state, Wisconsin. “That does nobody any good, and what I want to do is have a civil, good conversation with constituents, and that’s why I do all these different things, whether it’s planned tours, telephone town halls, office hours, and the rest.”