The Justice Department moved yesterday to revoke the citizenship of a 59-year-old Chicago man alleged to have been a guard at the infamous Nazi death camp at Treblinka in Poland during World War II.

In a suit filed in U.S. District Court in Chicago, the Office of Special Investigations argued that Liudas Kairys should lose his American citizenship because he concealed his more than two years of service in Nazi Germany's SS when he entered the United States as a displaced person in 1949 and when he became a U.S. citizen in 1957.

The Justice Department identified the Lithunian-born Kairys as an SS guard attached in 1942 to a unit in the Polish city of Lublin and in 1943 and 1944 to the death camp at Treblinka, which was hidden in a pine forest 62 miles northwest of Warsaw.

In number of murdered Jews, Treblinka ranked behind only auschwitz, Buchenwald and Dachau. The Polish government said after the war that Jews from more than 30 countries were brought to Treblinka, where at least 731,600 were gassed to death between December 1941 and July 1944.

Lublin, in eastern Poland, held one of Eastern Europe's largest Jewish ghettoes at the outbreak of World War II. By the end of the war, the ghetto was eliminated. An estimated 40,000 Jews had been deported to death camps or murdered on the spot in Lublin.

The suit said Kairys lied about his SS service when he applied in 1949 for a visa to emigrate from Germany under the Displaced Persons Act.

The suit quoted him as saying he had "worked on his father's farm in Lithuania from 1940 to 1945." In fact, the suit said, Kairys was assigned in July 1942 to the SS in Lublin, where "he was responsible for guarding inmates in SS camps and forced labor enterprises."

On being promoted to SS Oberwachmann (a guard corporal), the suit goes on, Kairys was "assigned to a guard detachment at the forced labor camp at Treblinka," where he served from March 1943 to July 1944 when the camp was liberated by the Russian Army.

The suit does not charge Kairys with the execution of Jews. It says simply that his service "constituted assistance in the persecution of Jewish civilian prisoners."

Justice Department sources refused to reveal how they tracked down and identified Kairys, who has lived and worked in Chicago for more than 20 years packaging candied popcorn. His name does not appear in books identifying ex-Nazis still at large nor on famed Nazi-hunter Simon Wiesenthal's list of wanted war criminals.

Yesterday's move to strip Kairys of his citizenship is a step toward deportation proceedings. By U.S. law, a citizen cannot be deported.