ATLANTA --- The $21 billion budget awaiting Gov. Sonny Perdue's signature devotes $1.2 billion to the state's prison system.

If signed as is, 2009 will mark the third consecutive year taxpayers have footed a billion-dollar bill to fund the Georgia Department of Corrections, now the fifth-largest prison system in the nation with nearly 60,000 inmates and more than 140,000 probationers.

Prison costs in the state show few signs of slowing, observers say, increasing the likelihood that prisons will soon face increasing competition for state funding alongside education, transportation and social services.

The Georgia Budget and Policy Institute predicts offenders sentenced between now and 2015 might add about $10.8 billion in capital and operating costs to the prison system's budget in that time. That would push the prison budget past the $9.8 billion the state currently spends on education.

While the rising costs have forced new approaches to the way the state punishes and rehabilitates inmates, corrections officials face the task of juggling the financial effects of longer sentences with the graying of the prison population, both of which push expenditures higher.

The advent of mandatory minimum sentences, an accompanying "two strikes and you're out" policy and more stringent parole guidelines enacted since the mid-1990s have created a surge in the state's prison population, with more people being put behind bars and remaining there longer.

The effect is that for every 18,000 prisoners headed out of prison each year, 20,000 take their place, said Paul Czachowski, the spokesman for the Department of Corrections. The population behind bars is forecast to continue that trend, he said.

Increases in the number of inmates put direct pressure on the cost of housing them.

State prisons have expanded capacity by more than 150 percent since 1990, according to the Department of Corrections.

One of the ways to diminish the prison population is to decrease recidivism.

In the past five years, an emerging trend is a push to prepare prisoners better for returning to society through job training and education.

"The old days of locking people up and throwing away the key just doesn't work," Mr. Czachowski said.

A new response to the prisoner increase is pre-release centers, where 200 select inmates serve out the final two to five years of their terms working 10 hours a day and attending classes to obtain general equivalency diplomas, Mr. Czachowski said. More room for more dangerous inmates is the result.

The prison system is also growing upwards -- the department is in progress with plans to add a third bunk to 1,000 beds.