A new jail cell can cost as much as a spiffy condominium -- anywhere from $50,000 to $75,000. But, unlike a condominium, it doesn't yield any tax revenues. Instead, it constantly demands tax dollars to pay for guards and other correctional services.

This is just one of the unpleasant facts the Fairfax County Board of Supervisors must face as it decides what to do about a jail it dedicated only three years ago -- and which is already jammed with at least 350 prisoners, or about 100 more than the 254 prisoners it was designed to hold.

Another unpleasant fact, for the supervisors at least, is that only last November Fairfax voters overwhelmingly defeated an $8.6 million bond issue to build 164 more of those expensive cells. The supervisors, with varying degrees of enthusiasm, had supported that bond issue.

Since then, the crowding has gotten worse, and Sheriff M. Wayne Huggins, the keeper of the jail, is warning anyone who will listen: Don't be surprised if the lid blows off.

Should the supervisors take their chances and try for another vote?

The board-appointed task force on jail alternatives has just completed a report that, in so many words, says yes, but with some important qualifications that weren't made the first time around.

The new report calls for expanding the jail by adding a 200-cell wing, building a 50-person, expandable correctin camp and creating about 60 other cells in the shelled-in basement. But those were only three of the 23 proposals that came out of nearly four months of meetings by task force members.

In fact, most of the task force recommendations covered options to jail, such as work-release programs, community service in lieu of sitting in a cell and drug and alcohol treatment.

If those options were implemented more aggressively, could Fairfax avoid costly expansion of its jail?

The task force report says no, but a close reading of the report suggests that the county has not been doing nearly enough to find alternatives to incarceration, where the highlight of an inmate's day might be watching his or her favorite soap opera on TV.

For example, Fairfax County has only 30 work-release slots. Montgomery County, with about the same population and similar demographics, has 100.

One member of the task force noted other jurisdictions offer a number of workable alternatives to jail, but they are not available in Fairfax "because the judges are not comfortable with them."

Commonwealth's Attorney Robert F. Horan Jr., who says the Fairfax criminal justice system is "alternatived out," says virtually everyone in jail is there because he or she has committed a serious crime, is a poor risk to be released on bond or has a history of criminal activity.

Yet a task force study of one day's population at the jail showed that of 111 prisoners awaiting trial on felony charges, 68 were charged with crimes against property, while another 38 were there on misdemeanor charges.

Even so, Horan would argue, and the task force study would agree, many of the first group were wanted for crimes committed in other jurisdictions or had a history of not showing up for trail. The point, he would argue, is that all 68 were exactly where they should be -- in jail.

But as Judith A. Johnson, executive director of the National Coalition on Jail Reform, asks: Couldn't some prisoners be released on bond, and then be carefully monitored to make sure they appear for their trials?

As to the 38 prisoners awaiting trial on misdemeanor charges, the task force concluded that "very few . . . were eligible for pretrial release programs." But should they be occupying cells that cost at least $50,000 to build and many more thousands to service?

Alternatives can be expensive because of the staff required to keep track of released prisoners and to provide the counseling that many of them desperately need. But incarceration demands staff too, plus those costly cells.

And it needs to be asked, how many prisoners are deterred from a life of crime by sitting in front of a television set for eight or 12 hours a day?

If the jail is expanded as the task force proposes, there will be room for about 500 prisoners. If the cells are there, you can be sure they will be occupied, just as the present jail filled up shortly after it was opened in February 1978.

With its new report ot the supervisors, the task force has opened the door to discussin of alternatives. But only barely. The subject deserves a lot more discussion and analysis before voters are asked to approve a bond issue to build $10 million worth of new jail cells.

If the voters are treated to the same demogoguery they were treated to last year, they may say no. Again.