For years some people have been saying that the Pentagon is top-heavy with military brass and weighted down by red tape.

Little did critics know, the place is literally sinking.

One of the world's largest office buildings is slowly slumping, not from bureaucratic weight but because of its foundation. A small part of the Pentagon is sinking into the swampy bank of the Potomac River on which it was built 43 years ago.

In the Officers Athletic Club, the floor dips as low as 12 inches in some places, reminding one Air Force major of waves. The lockers are the same height but stand in an uneven pattern, he said.

Basement corridors in the north and east wings of the labyrinthine complex have sunk an average of four inches, sometimes leaving long cracks.

"It's not something you can stand and watch, but with the vibrations and temperature changes, its gradually doing its thing," said Ken Craddock of the General Services Administration. "Over the years, it will continue to slump, a little at a time."

He estimated that sections of the Pentagon's basement floor are slipping a fraction of an inch annually.

The problem dates back to the crash building program of World War II when the 3.8 million-square-foot structure was designed during a single weekend and erected in just 16 months. To shore up the swampy site, contractors brought in 680,000 tons of dirt from the Potomac River flood plain. The fill turned out to be too wet and too loose.

Although the building is supported on piles driven deep into the subsoil, the concrete floor was laid directly on the ground. Over the years, the stomping weight of 25,000 employes squeezed water from the soil, which receded below the floor.

"As the fill slumps, the concrete slumps with it," said Craddock. But he stressed that the Pentagon's structure remains intact.

"The worst thing I can think of happening is someone tripping," he said. "There's no danger of something falling on someone."

GSA, which maintains the building for the Defense Department, first detected the problem in the 1970s and has been leveling off floors ever since. In methods known as "mudjacking" and "grouting," contractors have pumped in mud and concrete to fill in cavities covering 22,000 square feet, according to Craddock.

A private consulting firm hired by GSA completed a "Study to Stabilize Depressed Floors" two years ago, recommending that the floors be undergirded with concrete slabs propped up by piles. Costs have been estimated at $6.5 million.