More than 22,000 school buildings in the nation are inadequate and 13 percent of those are structurally unsound, according to a study released Saturday by the Education Writers Association.

The study found that one in four of the nation's 88,021 public school buildings need maintenance or major repairs, are overcrowded or obsolete, present environmental hazards or have multiple problems.Another third stack up as "only adequate and because of growing enrollments and deferred maintenance could easily become inadequate," said the study, called "Wolves at the Schoolhouse Door."

The study cites antiquated facilities, an enrollment boom and inadequate capital funds in concluding that "the schoolhouse may be the most seriously threatened part of the infrastructure."

The EWA based its findings on federal statistics, national surveys, surveys of school building personnel at 38 state education departments, state reports on school buildings and analyses of buildings in seven representative states.

One-fifth of the nation's schools were constructed more than 50 years ago, the association said. Nearly two-thirds were built in the 1950s and 1960s, "generally a time of rapid and cheap construction... Many construction experts say the buildings were intended to last only about 30 years. If so, their time is up."

The group said replacement costs for all school buildings are estimated at $422 billion. States estimate schools need $84 billion in new or retrofitting construction and $41 million in maintenance and repairs.

Many states and school districts are investing below the recommended level of 2 to 4 percent of replacement value in annual maintenance, the study found. Specifically it cited Maine, Minnesota, North Carolina and Tennessee with investments of 1.4 percent, 2.2 percent, 2.2 percent and 1.3 percent respectively.

EWA noted that a school building boom is under way. It cited Census Bureau statistics that school construction was up almost 50 percent from 1982 to 1986.