West German officials said Thursday they had arrested a former U.S. soldier in an "especially grave case" and charged him with espionage for selling secret documents to Soviet bloc intelligence.

The statement came after The New York Times reported Thursday that Swedish and West German authorities had arrested eight people involved in a spy ring that supplied the Soviet Union with secret military documents for at least 10 years.Chief federal Prosecutor Kurt Rebmann identified the American as Clyde Lee Conrad. Conrad has been sent to investigative detention following his appearance before a special panel of the West German Supreme Court.

Rebmann's statement said that Conrad had worked for the U.S. military for 20 years before his discharge in 1985. It said he was born in 1947, but did not give his home town in the United States.

Principals in the newly uncovered ring, which operated through a German-Hungarian connection, caused a major security loss to the United States in the late 1970s, according to the Times report.

Documents concerning NATO defense plans for Europe were believed stolen as well as the U.S. Army contingency plans for a ground war in Europe against the Soviet Union, the Times said.

It said the network was uncovered by West German and U.S. officials, including agents from the FBI and the Army. The Army has about 250,000 military personnel in West Germany.