WASHINGTON — An immigration judge ruled Monday that a retired auto mechanic in New York served the Nazis as a concentration camp guard during World War II and ordered him deported, the Justice Department said.

Michael Gruber, 84, of New City, N.Y., had admitted serving as an armed Waffen SS guard in Oranienburg, Germany, but denied any knowledge of the Sachsenhausen concentration camp there, the department said.

Gruber immigrated to the United States in 1956 but is a citizen of Austria. The government said it would seek to deport him to Austria, which must agree to accept him.

Citing captured Nazi documents found by the department's Office of Special Investigations, which hunts Nazis in this country, Immigration Judge Robert Weisel ruled that Gruber had served in the SS Death's Head Guard Battalion at Sachsenhausen.