At least 12 Mariel prisoners have apparently exhausted their administrative appeals and could be deported within days, but plans are in the works by prisoner advocates to block any deportations, a newspaper reported Thursday. Gary Leshaw, director of the non-profit Atlanta legal aid organization representing Mariel detainees, said he was informed by the Justice Department that there would be an announcement Thursday on the prisoners. Meanwhile, prisoner advocate groups in Miami and Atlanta plan to ask federal judges to stop the deportations, which if carried out would mark the first time Cubans have been deported to their communist homeland since May 1985, The Miami Herald reported. ``There is a chance if we all speak with one united voice here and explain the merits of our case,'' said Rafael Penalver, chairman of the Task Force of Cuban American Citizen Organizations. Penalver is a lawyer who helped negotiate the settlement to end riots by 3,800 Mariel detainees in Oakdale, La., and at an Atlanta prison last November. ``We will appeal to President Reagan. He can block the deportations, even if the people are sitting in an airplane at the airport.'' A special three-member Justice Department panel was created in the aftermath of the riots to review the cases of 113 Mariel detainees in federal prison in Talladega, Ala. In the past two months, the panel has looked at prison records, immigration history, written statements from the prisoners and other materials, but there have been no personal appearances by the prisoners or their lawyers. Deportations to Cuba were reinstated as part of a renewed immigration pact between the United States and Cuba that allows up to 20,000 Cubans and 3,000 political prisoners and their families to emigrate and, in return, the Cuban government will take back 2,500 prisoners. The Justice Department contends that these prisoners are criminals the Cuban regime injected into a boatlift of refugees from the port of Mariel. Prisoners selected for deportation are being taken from a list of Mariel inmates who were imprisoned at the time of the 1984 immigration pact. Jorge Mas Canosa, chairman of the Cuban-American National Foundation, acknowledges there is much division over the deporations, even in Dade County's Cuban exile community. He said the foundation favors letting Cubans apply for visas to immigrate to the United States but opposes the deportations to Cuba. ``I cannot in one hand denounce the human rights situation in Cuba and then support sending them back,'' Mas said.