Perhaps the single most disturbing fact in the sea of alarming data about the state of corrections in America is this: If current trends persist, within five years our largest state, California, will be spending more on its prisons than on its public universities.

Republican Gov. Arnold Schwarzenegger signed a law in the spring that will expand the state’s prison system by 53,000 beds, at a cost of $7.7 billion, on top of the current annual operating budget of about $10 billion. The California Legislature finally acted because three federal judges were about to act for it — by placing caps on how many more inmates it could squeeze into an already overcrowded system. There are more than 170,000 prisoners in the state’s prisons, which were designed to incarcerate 100,000. It’s so bad that all the areas set aside for activities related to rehabilitation — classrooms, gymnasiums and the like — have been converted to bunk-bed housing.

It isn’t as if the state has refused to expand its prison system. In the past 27 years, it has almost tripled the number of prisons. The Department of Corrections and Rehabilitation (the last two words were recently added to its title) has seen its budget increase by more than half in the past five years.

California is probably the most egregious example of a state corrections system out of control. For a lot of reasons — having to do with the passage of tough anti-crime laws, changes in sentencing policies, a dysfunctional parole system and an abandonment of any meaningful rehabilitation efforts — that state is in more trouble than any other. But it is hardly alone. A projection of what we are looking at nationally is sobering. Just such a forecast was released early this year by the Public Safety Performance Project, funded by the Pew Charitable Trusts, and the outlook is chilling.

Currently, there are almost 1.5 million inmates in federal and state prisons, plus almost another 750,000 in local jails. If trends continue, state and federal prisons alone will add 192,000 inmates in the next five years — a 13 percent increase, or more than triple the overall population’s expected growth rate in that time. The added inmates alone will cost $15 billion in increased operating costs and $12.5 billion in construction of new facilities. To put the size of our prison population in context, China imprisons roughly as many people as we have in our federal and state prisons (not counting the jails), but its population is more than quadruple the United States’.

The costs to taxpayers are staggering. National spending on corrections now exceeds $60 billion, almost seven times what it was in 1980. Running prisons is now the fourth-most-expensive program for states — after medical care, education and transportation. And in a way it has a more significant effect, since all of the corrections money comes from state coffers rather than federal grants. The average cost of housing an inmate in 2005 was almost $24,000, ranging from $13,000 in Louisiana to almost $45,000 in Rhode Island.

Like so many other trends in our public sector these days, this one is unsustainable. With health care and pensions, education and infrastructure needs and other fiscal pressures closing in on the states, they will have to find ways to imprison fewer people without allowing crime rates to rise. And we’re seeing some early efforts to do just that.

In effect, governors and state legislatures are going to have to be willing to acknowledge that their states can no longer afford some of the sentencing laws and correctional policies adopted in recent decades. In particular, they will have to re-examine the effectiveness of the “war on drugs,” since about a quarter of current inmates are serving sentences related to drug addiction or commerce — many of them non-violent crimes. Yet many drugs are plentiful and cheap, and the number of addicts is rising. Does it make sense to incarcerate them — or treat them? As of now, we’re investing very little in the latter.

Second, more than 95 percent of the people now incarcerated will go free eventually. Yet 60 percent of those who leave prison will be returned, most within three years. More of an effort will have to be made to help prisoners who have few skills or resources and little education return to their communities. Cities such as Chicago, Milwaukee and Minneapolis recognize the problem and are pursuing myriad programs to help.

Finally, overcrowding in prisons will have to be addressed if effective rehabilitation programs are to be given a genuine chance. So, it’s likely that some states will need to add more capacity in an effort to lower their prison populations in the long run. California, with a whopping 70 percent recidivism rate, finds itself in just that situation now.

Some states have made progress. Missouri has become a model for lowering recidivism among juveniles. Kansas, Illinois and even tough-on-crime Texas are experimenting with new programs that turn away from the traditional punitive emphasis and stress rehabilitation.

It’s too soon to tell what will work best and what won’t. But the course is clear: Any state that spends more on its prisons than its universities is a state in serious trouble.

Peter Harkness is the editor and publisher of Governing magazine, published by Congressional Quarterly Inc.