Fairfax County school officials said yesterday they are placing a moratorium on construction of new wooden "creative playgrounds," citing safety concerns, unexpectedly high maintenance costs and the possibility that they may not be able to insure the popular play areas.

More than three dozen of the timber playgrounds have been built in the county in recent years, with funds -- $20,000 to $30,000 for each one -- and labor donated by local parent teacher associations. The school system pays to maintain the playgrounds.

Proponents of wooden playgrounds -- which use telephone poles, tires and other materials to create maze-like structures -- say they offer children greater challenges than the slides and monkey bars of years past.

County officials said a consultant to the school system's insurance firm, The Hartford, recently questioned the safety of materials and design of creative playgrounds, raising concerns about officials' ability to secure coverage.

Doris Torrice, a deputy superintendent, said some creative playgrounds deteriorated "much more rapidly than had been predicted." Some problems were because of second-hand wood, nails used instead of stronger bolts and screws, and imperfect construction, officials said. However, Torrice said she was not aware of any serious accidents at any of the playgrounds.

The county has incurred maintenance costs of as much as $5,000 on at least one of the playgrounds -- at Fox Mill Elementary in Herndon.

Robert S. Leathers, an Ithaca, N.Y., architect who supervised work on most of the creative playgrounds in the county, said his play areas built in the last three or four years have been put together with stricter standards and better materials than earlier ones constructed of "scrounged" wood.

Three elementary schools with playgrounds in progress, Cunningham Park in Vienna and Pine Spring and Timber Lane in Falls Church, were allowed to go ahead if they wished. The schools' PTAs, warned that there is a chance the playgrounds would be torn down, voted to continue work.

For the first time, school inspectors are checking construction materials at the three playground sites, which has led to the rejection of some second-hand telephone poles at Pine Spring. The inspectors are stationing themselves at the locations during construction. In the past, the county inspected the play areas only after completion.

Reaction among PTA officials was mixed. "The county should have done this several years ago," said Mariann Berge, who heads the Cunningham Park playground committee, which is using stricter construction standards than the county previously required.

But Maureen H. Tuttle, coordinator of the Timber Lane playground committee, said research shows that the wooden playgrounds are safer than standard play areas. "If they're going to say no to this . . . let's hope they come up with a very good alternative that they are going to bankroll," she said.

Torrice said the building moratorium will remain in effect "until we get some of our questions answered."