The Justice Department has agreed to remove from the Immigration and Naturalization Service the power to designate which Mariel Cuban detainees may remain in the United States, Rep. Pat Swindall (R-Ga.) said. Deputy Atty. Gen. Arnold Burns on Friday is scheduled to outline the format for the individual reviews for the Cubans promised by Atty. Gen. Edwin Meese III during prison uprisings by the detainees in Atlanta and Oakdale, La. A Justice Department spokesman, Terry Eastland, declined to comment on Swindall's remarks, saying Burns would disclose the plan. A major element of the agreement that ended the Atlanta siege called for "full, fair and equitable hearings" for the detainees on their possible release.