OUR CITY'S prisons continue to overflow. Yesterday, they housed more than 8,658 inmates, some triple-bunked into cells designed to hold two.

One way to reduce the number is to loosen the judicial filter that determines who goes to jail and provide an alternative to locking up those who are charged with minor crimes, who can't put up bail, or who violate terms probation or parole.

City and prison authorities believe "day reporting centers" may hold the answer. These are centers where offenders report in two or three times a week and get help with alcohol and drug treatment, job and survival skills, and more. A pilot program in the city is scheduled to start next spring, to serve 125 defendants.

This is good news, as long as the program is funded in a way to make a difference.

Day reporting centers were conceived in Great Britain in the 1970s to provide basic skills and services to chronic, nonviolent offenders. These offenders were being regularly locked up, not because they were public threats, but because of drug addictions and their lack of jobs or survival skills.

The United States became interested in such centers in the mid 1980s, when mandatory sentencing and drug laws helped fill the prisons and jails, and stretched the corrections system's resources so dramatically. Such centers could reduce the prison population, focus resources more intently on rehabilitation efforts and monitoring. And lower costs.

It costs about $88 a day to house and care for an inmate. The city has proposed to pay $35 per day to companies that might want to run the program.

The need to open a relief valve on Philadelphia's prisons is great. A large number of inmates, perhaps 3,000 of the total, are being held for low-level crimes or parole or probation violations.

A Temple University study released last year laid some of the problem on ineffective pre-trial- release guidelines and the increased jailing of individuals for preliminary arraignments.

In a city struggling with overcrowded prisons and small-time criminals who lack life skills, day reporting centers can offer a positive alternative.

But we urge that this project be adequately funded. The city's homicide rate is being driven in part by a scarcity of funds for the probation and parole system. Too many offenders lack the help to keep them on the straight and narrow. *