THE phenomenon of prison overcrowding has little to do with the crime rate, which in recent months has been declining in the United States. As judges sentence more people to prison, and as prison terms grow longer, populations rise.
The political and mental roots of the problem, however, are varied and deep. They range from sentencing and demographic changes to sensational news reporting - which breeds fear.
Most experts agree that the mental obstacles will be the toughest to surmount. One top prison official may have articulated the heart of the problem when he wrote of the need to develop entirely new sentencing options: ''Guilty persons who are not imprisoned are popularly viewed as having escaped punishment altogether.'' Sanctions for nonviolent offenders, he concludes, must avoid the massive costs - financial and social - of traditional prisons, while packing enough wallop so that ''the proper public sense of justice is not outraged.''
New sanctions based on these criteria are springing up and are being closely watched by those in the profession. One pilot project, developed by the Federal Bureau of Prisons, is a 30-bed Washington, D.C.-based community prison run by Hope Village, a private, for-profit vendor. It provides a residential setting where selected nonviolent offenders can serve sentences of up to one year.
The community prison is not a halfway house. Prisoners are confined, just as they would be in a minimum-security prison with one exception: They are allowed to hold outside jobs - often jobs held before sentencing - and they perform eight hours of community service each week. Prisoner payments, based on a sliding scale, offset the $34-a-day program cost. The program also enforces court-ordered family support and restitution payments for victims.
The goal is to provide an alternative setting where offenders can serve out their sentences while ''maintaining the economic continuity of their lives,'' says John Minor, the bureau's official in charge of community programs.
Punishment, he adds bluntly, is also part of the goal. ''But we're not talking about Simon Legree.'' Mr. Minor says the bureau's position is that the white-collar or property offender can be punished without costly, high-security confinement.
Minor views community prisons as ''ideally suited for counties and cities trying to deal with drunk-driving cases,'' because the concept offers punishment without mixing drunk drivers and hardened criminals. It also means, he adds, ''that families wouldn't suffer'' by being deprived of the breadwinner's salary. A second community correction center opened in Detroit in September. The bureau hopes to open a third next year. Community prisons are only the latest addition to the bureau's arsenal of community programs. A pioneer in such options, the bureau launched its first halfway houses in 1961 and now has 2,700 inmates in halfway houses.
Cost savings are substantial. In 1982, institutional care cost the bureau $35 .27 per inmate per day. This versus $28.30 in a halfway house, saving more than 500-bed prisons to house the 2,400 inmates maintained in community programs.
But the bureau's use of halfway houses has less to do with cost than with the agency's commitment to the public benefits that accrue when offenders go through a ''decompression period'' and are helped to become economically self-sufficient before parole, Minor says.
''Follow-up research shows that employment is the single biggest determinant of whether offenders stay out of further trouble,'' he notes. He adds that inmates placed in halfway houses found jobs more easily - and earned more money - than inmates released directly to parole.
Minorities, women, and young offenders - who have the most trouble finding work and the highest rearrest rates - benefit most from halfway-house placement, the research showed.