National Micronetics said it will close a plant.

The San Diego-based company said write-offs from the closing of Poly-Disc Systems in Torrance will push its fiscal 1985 losses to as much as $30 million. The plant, which makes coated disks for computer disk drives, has about 60 employees. Ten managerial and technical people will be shifted to the company’s San Diego operation. The suspension will prompt a write-off of at least $15 million, which will mean a loss of between $25 million and $30 million for the year ended June 28, according to Chairman Ned W. Buoymaster.