The astonishing drop in Philadelphia's prison population over the last year has provided the lone bright spot in this year's city budget, saving at least $9 million and highlighting what appear to be groundbreaking changes in the way courts and prisons operate.

At 8,424 inmates on Monday, the city jails held 1,430 fewer prisoners than at the daily peak of 9,854 reached in January 2009.

That's still a far cry from the system's designed capacity of 6,910 that has drawn lawsuits on prison conditions and overcrowding. But the shrinking number of inmates has heartened judges who want to move defendants through the system more efficiently. It has allowed the city to stop sending prisoners to New Jersey. And now top officials are talking not about building prisons, but closing one or more of the city's six facilities.

Just how much a falling crime rate - overall crime fell 10 percent between 2007 and 2009 - is responsible for the drop is not clear. The number of inmates entering the city's prison system each month fell by 121 between 2008 and 2009, according to city figures, but decreases in crime and arrests do not always correspond directly to shrinking prison populations.

It does appear, officials and even critics say, that reforms undertaken to shorten unnecessary jail stays for nonviolent, low-level offenders, have made an impact.

"They finally made a concerted effort," said University of Pennsylvania Law School fellow David Rudovsky, who has spent four decades suing the city for its overcrowded prisons. "That's a significant reduction . . . I think it's been done without any risk to public safety, and I think the people who have gotten out should be out."

Rudovsky's 2006 lawsuit on behalf of 11 inmates resulted in a federal judge ruling in 2007 ruled that the city prison system was so overcrowded that it violated the Constitutional rights of inmates.

Philadelphia Prisons Commissioner Louis Giorla is encouraged, but he refuses to celebrate unless the numbers hold up through seasonal swells in population from the late spring to early fall (record snowfalls in December and February helped drive prison admissions way down this winter).

"These fluctuations in the population have been beneficial," said Giorla, who was able to reduce his budget this year from $249 million to under $240 million. "But they are also somewhat of a mystery."

Some of the math is easy. An agreement between the District Attorney's Office and the state Department of Corrections led to the transfer of 250 inmates serving state sentences from the city to the state.

That helped the city to get out of contracts in Monmouth and Passaic Counties in New Jersey for which it paid more than $12 million between 2006 and 2009.

Giorla estimates that another 430 prisoners have been transferred or are awaiting transfer to the state prisons based on 2008 state legislation designed to send serious offenders to the state for incarceration and treatment.

That legislation directs judges to send anyone sentenced to two or more years on state charges will go directly to state prison, and some of those defendants are being diverted to the state each day.

In addition, state prisoners who were once transported from other state prisons to Philadelphia to await resolution of their cases here are now moved to the nearest state facility - usually Graterford Prison in Montgomery County - and bused in from there.

Giorla said the transport rule alone accounts for 50 prisoners a day not in his custody.

These state reforms may have diverted as many as 1,000 prisoners thus far, according to deputy District Attorney Sara Hart, who pushed for their passage. They have also contributed to swelling the state's prison ranks.

On the local level, Common Pleas Court has been aggressively resolving cases of inmates who are in jail mostly because they are awaiting a hearing, many for minor parole or probation violations. Some of these changes were recommended as part of a Temple University study in 2006 and also advocated by former city Prisons Commissioner Leon A. King II.

Philadelphia Common Pleas Court President Judge Pamela Dembe may have contributed to the decline with a simple e-mail last year. In it, she asked judges whether they would object to Philadelphia's practice in which judges no longer sitting on the criminal bench would hold on to their old criminal cases.

That meant that a judge who moved to civil court would have to schedule one day a month to hold hearings on parole and probation violators they once sentenced. Often, their docket was so long that hearings would get bumped to the next month, meaning one defendant who violated probation might have waited 60-days in jail for a hearing that set him or her free.

"The myth was that judges become very possessive of their cases," Dembe said, but the response to her e-mail refuted it. "There was no resistance."

Now those cases - technical parole and probation violators, who often languished in city jails awaiting hearings for weeks or months because they failed a urine test - are now being moved swiftly through the system.

Defendants who waited an average of 30 days for a hearing are now getting one in five days, said Joseph Lanzalotti, deputy court administrator for the Common Pleas Trial Division.

In addition, individuals with multiple cases before multiple judges are now able to resolve all their charges before one judge. Those cases are now consolidated before one judge, Common Pleas Court Judge Joan A. Brown, for resolution in one day instead of a series of hearings that kept them in city custody for weeks or months.

"Those are really attacking what had been the drivers of the prison population," Hart told the city's top criminal justice figures last week at a meeting of the Criminal Justice Advisory Board, where many of these reforms are being implemented by the city's top law enforcement and court officials.

Last week's meeting included District Attorney Seth Williams, Police Chief Charles H. Ramsey, President Judge Dembe, Deputy Mayor for Public Safety Everett Gillison, the Defender Association, and court administrators, among others.

Lanzalotti sends out a calculation each month for the days saved by the programs, and counted 8,755 days in January and February, for a total of nearly 69,000 days saved since the programs began in March 2009. And that does not factor in the increased use of video hearings, which save in time and transportation costs as well.

Those figures do not translate directly to days in jail saved - some defendants are sent right back into custody. But they certainly represent shorter jail stays for some inmates being held on the taxpayers' dime before a status hearing.

That often includes women held on relatively minor drug or prostitution charges and violations. The length of stay for female inmates in 2009 was 56 days, the lowest figure since 2000. There were 713 women in the system on March 31, a 21 percent drop from the same date in 2009, when 902 women were in the system.

Dembe said the system needs to drive the female population down by only 20 beds to close one of the women's facilities. Reductions thus far have helped to cut overtime, but not staff, and it is in the hard costs of staffing and maintaining prison buildings that offer real chances for savings.

Robert Eskind, a prison spokesman, said officials are not quite ready for that step.

"We want to see sustained reduction in that population before we alter the program," Eskind said. "We're close, but we're not there yet."

An in-depth 2006 study by Temple's Crime and Justice Research Center found noted that the population exploded from 5,026 in 1995 to 8,541 in 2005, a 70 percent increase. Much of it was driven by inmates held on bail awaiting trial.

And it only went up from there.

John Goldkamp, chairman of Temple University's Department of Criminal Justice and lead author of the 2006 study, was also wary of declaring any victories, especially with state prison populations falling across the country.

A study released by the Pew Charitable Trusts in March found the first national decrease in state prison populations since 1972, much of the decrease attributed to the targeting of low-level, nonviolent offenders for release.

"Any developments that have gotten us to reduce the population from its extraordinary highs of the last year or so are good and helpful and need to be institutionalized," said Goldkamp. "It's a good opportunity to make the adjustments that can be put in place in anticipation of more difficult days ahead."

Dembe said the justice system has little choice but to act in the face of the city budget crisis.

"We were seriously looking at having to close the courts and lay off people, and we just knocked ourselves out working to prevent that," Dembe said. "We got within 10 days of not being able to make payroll for 1,800 people, and I never want wo be that frightened again."

Contact staff writer Jeff Shields at 215-854-4565 or jshields@phillynews.com.