Gov. Matt Bevin of Kentucky, a Republican, has said that if he ultimately loses in court, he will end the Medicaid expansion in Kentucky. But instead of announcing plans to appeal the ruling Friday, the state’s top health official said he would work with the Trump administration to “quickly resolve the single issue raised by the court so that we can move forward.” The official, Adam Meier, added that if the new rules could not be quickly implemented, “we will have no choice but to make significant benefit reductions.”

Seema Verma, chosen by President Trump to run the Centers for Medicare and Medicaid Services, called the decision “disappointing” and said she would confer with the Justice Department “to chart a path forward.”

The debate over requiring poor people to work to keep their health insurance encapsulates fundamentally different visions of the role of Medicaid, a program jointly funded by federal and state governments that now covers one in five Americans. Many Republicans see it as a welfare program that should be conditioned on participants working if they are able, while Democrats consider it a crucial element of the government safety net for the poor.

Requiring Medicaid recipients to work — and to pay monthly premiums, which was also part of Kentucky’s plan — would have significantly reduced the number of people with coverage, many experts predicted. People could lose their health benefits if they were deemed able to work or volunteer but did not, or were unable to keep up with premium payments or provide the documentation every month to prove they had worked the required 80 hours.

Mr. Bevin, a vocal opponent of the Affordable Care Act, took office after his Democratic predecessor enthusiastically expanded Medicaid under the law. He has argued that the program was created for only the most vulnerable citizens — those who aren’t merely poor, but also disabled, elderly, pregnant or younger than 21. Mr. Bevin and a growing number of mostly Republican governors believe that adults with no disabilities, millions of whom became eligible for Medicaid under the health law, should work or otherwise engage in their community to keep their coverage.