The number of convicted felons serving some kind of life sentence has rocketed to 127,000 nationwide - an 83 percent jump since 1992. More than a quarter of them are ineligible for parole.

The increase is a result of the 1990s - call it the "get tough" decade - during which an expansion of mandatory minimum sentences, three-strikes and truth-in-sentencing laws lengthened prison sentences and limited parole options. Indeed, the average lifer now spends 37 percent more time in prison than a decade ago, up from 21 years to 29 years.

The findings are from a first of its kind, 50-state study of "lifers" conducted by the Sentencing Project, a criminal justice reform think tank in Washington.

"These sentences are having a very significant impact on the size and costs of incarceration," says Marc Mauer, the assistant director of the Sentencing Project and one of the report's authors.

"Every time a judge makes a determination to sentence a person to life, conservatively speaking it will cost $1 million to keep them locked up for life. If that person is Charles Manson, few people will have a problem with that. On the other hand, if it's a battered woman who strikes back at her accuser and kills him, that presents a different set of questions."

Supporters of such "get-tough" policies credit the fact that so many more felons are locked up for life with helping to bring the crime rate down 35 percent during that same period. To them, the study shows the policies have been a clear success.

"What we're seeing is the high crime rates we suffered starting in the 1960s caused public policymakers to finally realize one contribution they could make toward restoring law and order is to increase the number of serious and violent offenders in prison and also to increase the sentences which they serve," says Dave Muhlhausen, senior policy analyst at the Heritage Foundation. "It's worked."

But critics contend that their inflexibility has crowded the country's prisons with juveniles, indigents, battered women, and mentally ill inmates. The study estimates that 23,500 of the nation's "lifers" suffer from mental illness.

In California, almost 60 percent of the lifers in a three-strikes conviction are serving the time for a nonviolent offense.

For corrections officials, those that have to cope on a daily basis with housing, feeding, guarding, and providing medical care to the increasing numbers of long-term inmates, the study just brings home the challenges they face in finding a way to pay for it all.

"Given the budget crisis it's a challenge to get the resources," says Joe Weedon, director of government affairs for the American Correctional Association in Lanham, Md. "You have to reexamine everything that you're doing to find the money to fund the healthcare in particular, which is the fastest growing expenditure within a facility."

Some prisons have privatized medical facilities to save money, others have invested in new technologies to try to cut down on staffing. And state legislatures around the country have been implementing reforms, modifying some of the mandatory sentencing laws to allow for more flexibility, and increasing funding for reentry programs in an effort to cut down on recidivism.

In states like New York, those moves have been instrumental in keeping the prison population in check. But reform advocates and some corrections officials worry that the savings generated by the recent changes could easily be overwhelmed by the increasing costs of maintaining the record number of lifers.

"If these 'lifer' trends continue, they're very likely to overwhelm any reform that takes place," says Mr. Mauer.