WASHINGTON — Attorney General Jeff Sessions on Monday made it all but impossible for asylum seekers to gain entry into the United States by citing fears of domestic abuse or gang violence, in a ruling that could have a broad effect on the flow of migrants from Central America.

Mr. Sessions’s decision in a closely watched domestic violence case is the latest turn in a long-running debate over what constitutes a need for asylum. He reversed an immigration appeals court ruling that granted it to a Salvadoran woman who said she had been sexually, emotionally and physically abused by her husband.

Relatively few asylum seekers are granted permanent entry into the United States. In 2016, for every applicant who succeeded, more than 10 others also sought asylum, according to data from the Department of Homeland Security. But the process can take months or years, and tens of thousands of people live freely in the United States while their cases wend through the courts.

Mr. Sessions’s decision overturns a precedent set during the Obama administration that allowed more women to claim credible fears of domestic abuse and will make it harder for such arguments to prevail in immigration courts. He said the Obama administration created “powerful incentives” for people to “come here illegally and claim a fear of return.”