In an age of austerity, everything will inevitably get recast as a budget issue. Case in point: The Urban Institute is out with a new report about how the federal prison system needs to be reformed — in part because it's on an unsustainable fiscal course.

Some context: The federal prison population is about 218,000. That's only a small fraction of the 2.2 million prisoners in the United States (most of whom are in state prisons or county jails). But the number of federal inmates is growing fast, having quadrupled since 1980.

And housing all those prisoners isn't cheap: The average minimum-security inmate costs $21,000 per year, while the average high-security inmate costs $33,000 per year. All told, the Obama administration has requested $6.9 billion for the Bureau of Prisons in fiscal year 2013.

In the context of trillion-dollar deficits, that's not a ton of money. But the Urban Institute points out that federal prisons will keep taking up a bigger and bigger chunk of the Department of Justice's budget — rising to 30 percent by 2020. Since Congress is trying to rein in overall spending, that means prisons will end up crowding out other Justice Department priorities, such as federal investigators or support for state and local governments. Many of the latter programs arguably do much more for public safety than prisons do.

So is there anything to be done? The folks at the Urban Institute think so. A good deal of the rapid increase in the federal prison population has come from longer sentences — particularly for drug offenders:

There's more detail here (pdf). About 32 percent of the growth has come from longer prison sentences for drug offenders. The report notes that Congress would likely need to change sentencing guidelines if it really wanted to curtail the growth of federal prisons. Congress did a bit of that in 2010, reducing the sentencing disparity between crack and cocaine crimes.

But there's a lot more that could be done. For instance, states like Hawaii are starting to rein in their prison costs by experimenting with smarter parole and probation policies. This is an even more urgent fiscal issue for states — as the graph Sarah Kliff posted shows, corrections still take up a massive portion of state budgets. The Urban Institute argues that Congress could learn from many of these state-level initiatives.

Is that worth doing? In The New York Times recently, John Tierney had a long piece compiling all the various arguments that the United States locks up far too many people in prison for far too long. Here's one key bit: "Some social scientists argue that the incarceration rate is now so high that the net effect is 'crimogenic': creating more crime over the long term by harming the social fabric in communities and permanently damaging the economic prospects of prisoners as well as their families."

That's hardly a new development — social scientists and criminologists have been railing against the high incarceration rate in the United States for many decades. But now that both Congress and the states are facing new budget constraints, the hope is that all these arguments will get yet another look.

Further reading:

--Jim Webb held some key Senate hearings on the need for prison reform back in 2007, but the issue never became a top priority.

--Mark Kleiman explains how smarter parole and probation policies can cut the U.S. incarceration rate.