Does the Reagan administration believe that every neighborhood in Washington must have its own prison? Or that there's no limit to the number of people around here who should be locked up? You begin to wonder, given the games that the Justice Department is playing with both the local government and Congress over prisons. Every time anyone turns around, officials at Justice raise the prison bed-count -- way above and beyond what the city and Congress understood was the price for resuming temporary federal help in relieving overcrowding. What's going on? The administration's prison-bed math is wild; the Senate deserves some explanation from Justice of these outlandish demands -- and this morning there's an opportunity to demand one.

Sen. Arlen Specter of Pennsylvania -- who, more than anyone, was responsible for winning federal money and land to build a necessary new prison facility in the city -- will conduct another hearing on the matter, and Justice officials are scheduled to appear. That's a step up from the last hearing in March, when department officials claimed they needed more notice before they could agree to testify. But now the administration is demanding what it cryptically calls a "parallel effort" by the city before it will end its moratorium on taking inmates in federal facilities.

Justice is pressuring the city to come up with yet another correctional facility or facilities -- with room for perhaps 400 more inmates than what Mayor Barry already has agreed to accommodate with a new prison and additional modular facilities at Lorton. It all adds up presposterously:

As of last Friday, the city had a total of 6,477 places in the jail, at Lorton and in community centers, halfway houses and other institutions.

Already, the city plans to go ahead with a new prison for perhaps 800 inmates.

In addition, the city is providing 400 more temporary spaces at Lorton, another 140 or so in two remodeled cellblocks and perhaps 100 more in small centers already in operation.

That's 1,440 more places, added to 6,477 -- you're talking 7,917 places.

Now Justice is talking about yet another prison for at least 400 more inmates: that comes to a grand -- and expensive -- total of some 8,300 spaces, at $16,000 to $20,000 a space just for operations.

It took some doing, but Mayor Barry is committed to the building of a new prison -- and a deal's a deal. The Reagan administration should stop trying to raise the ante and instead uphold its end of what everyone in Congress and city hall believed in good faith to be the bargain.