Lorton-based Terrafreeze Corp. is systemically freezing soggy soil under the National Theater and a nearby small, vacated tavern to prevent damage while a foundation is built for a large office building next door.

Described by Executive Vice President John Shuster as a company "unique in the U.S. and doing nothing but ground freezing," Terrafreeze is a subsidiary of Deilmann-Haniel of Dortmund, Germany. Shuster said that the earth-freezing patent is a hundred years old and that the service usually is performed at mine sites.

"But it was also used to solve a subway construction flooding problem for Metro under the Flagship restaurant," he added.

Shuster said that Terrafreeze got a $40,000 contract to freeze the soil under the small Curtain Call restaurant and the historic National Theater when excavation for the new office building at 13th Street and Pennsylvania Avenue NW caused or threatened structural problems with the restaurant - scheduled to be razed. The theater will be preserved as a part of a major Pennsylvania Avenue redevelopment project in the same block.

Lester Melling, an executive with the general contracting firm - Salus Corp., a subsidiary of Maritime International, - said that the Terrafreeze contract was let primarily to protect the underpinning of the National Theater and that ground movement was stopped. He also said that an injuction against construction sought by the owner of the Curtain Call was denied in court.

A part of the overall program of the Pennsylvania Avenue Redevelopment Corporation, the building at 1301 Pennsylvania Ave. NW is a project of Quadrangle Development Corp., which along with Marriott and the Rouse Co. will be the developer of the $110 million office-hotel-commercial project in the block.

Because the 1301 Pennsylvania construction site has a mushy mix of clay, silt and fine sand, the foundation subcontractor, Steele & Moroney of Alexandria, was unable to use only conventional beams and wood to support the nearby buildings while the excavation was dug.

Therefore, Terrafreeze was called in. CAPTION: Picture, Workmen dig foundation amid cooling lines near National Theater. By Gerald Martineau - The Washington Post