PHILADELPHIA -- The city of Philadelphia has pledged to put up more than $150,000 bail to free at least 300 inmates in an effort to ease jail overcrowding, but prosecutors and finance officials are challenging the plan.

The city has until Dec. 31 to pay bail for inmates awaiting trial, according to the arrangement approved by U.S. District Court Judge Norma L. Shapiro. Officials said it would be the first direct use of tax dollars to bail out prisoners in the city.

Officials said yesterday that prisoners could be released beginning Dec. 1, at the rate of 10 a day, from the city's four jails.

City Controller Joseph C. Vignola ordered a review of the legality of using taxpayers' money as bail. And District Attorney Ronald D. Castille called the proposal a "sham contract."

The city devised the bail plan because it is unable to meet a Monday federal deadline to reduce its jail population to 3,750. At midweek, city jails held 4,072 inmates, according to Richard J. Gold, chief deputy city solicitor.

Shapiro said she will review the program Dec. 18. If it has not achieved its goal by Jan. 4, when a hearing is scheduled, she will impose a moratorium on admissions of all but the most dangerous inmates, she said.

Only inmates held in lieu of not more than $5,000 in bail are eligible for the program.