The Justice Department ordered border authorities yesterday not to let 14-year-old Walter Polovchak, who left home rather than return to the Soviet Union with his parents, out of the country while his case is appealed through the courts.

Spokesman Art Brill said Attorney General William French Smith had signed a "departure control order" barring the boy's exit from the country for the time being.

Polovchak's attorneys had said a Dec. 30 ruling by the Illinois Court of Appeals meant the youngster could have been "taken by Soviet representatives in the United States and returned to the Soviet Union."

Brill said the action was taken "at least in part because of fears that an attempt may be made to remove him involuntarily." Brill declined to comment on what evidence there was that anyone was planning such a move.

The order was sent to all offices of the Immigration and Naturalization Service and all airlines flying out of the country.

Walter's parents emigrated to the Chicago area from the Soviet Union in January, 1980. They returned to the Soviet Union that September, but Walter insisted on staying in the United States. He now lives with court-appointed Ukranian foster parents in Chicago.