The possibility that local school yards might be encumbered with pre-fab classrooms should send every parent -- and every resident concerned about his community's and his city's future -- to the telephone, the computer, the fax machine, and, if necessary, the picket line to let their public officials know that they won't tolerate solving one problem by creating another.

Where ever these classrooms-in-a-hut have been built as "temporary" solutions to overcrowding, they have remained, becoming educational slums that have robbed generations of children of their playgrounds. District 10 Superintendent Irma Zardoya acknowledges that once built they are "virtually permanent" structures, since it can cost up to a quarter of a million dollars to dismantle just one.

As the history of PS 122 in Kingsbridge Heights demonstrates, these huts do not even fulfill their stated purpose. Its "temporary" classrooms simply allowed school officials to cram still more children onto the register, until at one point the elementary school groaned under twice the load it was built for. Then it failed.

High on the list to receive "transportables," as the Board of Education calls that latest generation of pre-fabs, is the Sheila Mencher Van Cortlandt School, PS/MS 95. The Van Cortlandt Village school already has the dubious distinction of being the most crowded school in the Riverdale-Kingsbridge area this year. It will shortly have a new principal, who, if the plan is carried out, will not only have to administer three buildings -- PS/MS 95 uses two annexes -- but classroom huts, as well.

PS7, PS 24, and the Robert Christen School, PS 81, may also be asked to sacrifice their school yards, according to District 10 administrators. All are crowded, but not so crowded that they need pre-fabs to accommodate their own students. But district administrators warn that so many schools elsewhere are jammed that they may turn to bussing the overflow to ease the crunch.

These local schools are lower on the list than some others in District 10, but Riverdale and Kinsgbridge residents should not breathe a sign of relief. Two and half years ago, School Board President Charles Williams threatened to place portable buildings at PS 81, with a kind of glee that Riverdale's schools could be made to suffer. His perverted logic suggested that there was something wrong with any school being in better shape than the worst school.

In a classic bit of bureaucratic double-speak at an election-eve press conference, Mayor Rudolph Giuliani told Press school reporter Pam Frederick that "Transportables are a good transition solution and are far better than people realize. It's a conceptual problem rather than a reality problem."

If what the Mayor means is "People think it's a bad thing to destroy playgrounds, but it's not really," his response would not be surprising from a man who doesn't believe after-school recreational programs matter.

Nevertheless, school yards are valuable not just during the school day but as a resource for the entire community after school lets out. In fact, PS 81's school yard was built in a three-cornered partnership among the Board of Education, the Parks Department and Riverdale Neighborhood House in recognition of the fact that the space was a resource not just for the school but for the entire community.

Despite the opportunities for price-gouging, bungling and corruption that leasing classroom space entails, leasing is a far better solution than building trailer-park classrooms that will rob entire communities of recreational space and accelerate the flight of the middle class from the public schools, and, perhaps, from New York City altogether.

It is time for city and school officials to treat the overcrowding crisis with the same urgency with which they treated the asbestos crisis of a couple of years back. That means a crash program to create new schools, not finding more and more ways to cram students into existing schools so that they swell and swell until they destroy themselves.