The Obama administration is trying to overhaul the criminal justice system by allowing prisoners who meet certain criteria to be released early through clemency and urging prosecutors to reserve the most severe drug charges for serious, high-level offenders.

At the same time, the U.S. Sentencing Commission, an independent agency, has made tens of thousands of incarcerated drug offenders eligible for reduced sentences.

But until more elderly prisoners are discharged — either through compassionate release programs or the clemency initiative started by then-attorney general Eric H. Holder Jr. last year — the government will be forced to spend more to serve the population. Among other expenditures, that means hiring additional nurses and redesigning prisons — installing showers that can be used by the elderly, for instance, or ensuring that entryways are wheelchair-accessible.

“Prisons simply are not physically designed to accommodate the infirmities that come with age,” said Jamie Fellner, a senior advisor at Human Rights Watch and an author of a report titled “Old Behind Bars.”

“There are countless ways that the aging inmates, some with dementia, bump up against the prison culture,” she said. “It is difficult to climb to the upper bunk, walk up stairs, wait outside for pills, take showers in facilities without bars and even hear the commands to stand up for count or sit down when you’re told.”

For years, state prisons followed the federal government’s lead in enacting harsh sentencing laws. In 2010, there were some 246,000 prisoners age 50 and older in state and federal prisons combined, with nearly 90 percent of them held in state custody, the American Civil Liberties Union said in a report titled “At America’s Expense: The Mass Incarceration of the Elderly.”

On both the state and federal level, the spiraling costs are eating into funds that could be used to curtail violent crime, drug cartels, public corruption, financial fraud and human trafficking. The costs — as well as officials’ concerns about racial disparities in sentencing — are also driving efforts to reduce the federal prison population.

For now, however, prison officials say there is little they can do about the costs.

Edmond Ross, a spokesman for the Bureau of Prisons, said: “We have to provide a certain level of medical care for whoever comes to us.”