A Roman Catholic priest and a Seventh-day Adventist minister held for 11 days by U.S.-supported rebels in Nicaragua sent a message that they are free. Father Enrique Blandon radioed from Waslala, 118 miles north of Managua, that he and the Rev. Adolfo Tiffer have been released. He said their contra captors had threatened them with death and taken them on forced marches for six to seven hours a day. Meanwhile, Marta Sacasa, speaking for the contras, said in Miami that Paul Alan Fisher, a Mill Valley, Calif., human rights activist captured last week, will also be released "as soon as there are secure circumstances."