Attorney General Dick Thornburgh submitted to a polygraph examination in connection with an internal leak investigation that Thornburgh initiated, the Justice Department said yesterday.

Thornburgh took the test voluntarily, reportedly last fall, and passed, a department spokesman said. He is believed to be the first attorney general to submit to a polygraph test.

The Federal Bureau of Investigation used the exam as part of an attempt to determine who was the source of an CBS News story about an FBI probe of the office of Rep. William H. Gray III (D-Pa.), now House majority whip. Department officials have said the FBI's inquiry and subsequent internal reviews provided no basis for criminal prosecution or administrative penalties.

In the past, Thornburgh has vowed to seek out and prosecute any department employee who leaks information about a criminal investigation. But he has said that in retrospect, the Gray inquiry was probably not worth the effort or expense.

Two of Thornburgh's closest aides became subjects of the leak inquiry. Executive assistant Robert S. Ross Jr. and press spokesman David R. Runkel provided deceptive answers on polygraph exams.

Department officials have said the reassignment of both men to less sensitive jobs earlier this month was not related to the results of the Gray probe.