Three African National Congress guerrillas, among them one of the most senior ANC leaders tried in 25 years, were sentenced to lengthy prison terms Monday in Johannesburg, South Africa, for treason and terrorism. a 20-year sentence for treason was issued to the most prominent defendant. Ebrahim Ismail Ebrahim, 51, who was abducted from Swaziland in 1986 by men he said were South African agents. He has been widely described as the highest-ranking ANC official to go on trail since Nelson Mandella and several colleagues were sentenced to life imprisonment in 1964. Another defendant, Mandla Maseko, received a 23-year sentence for treason. The other, Simon Dladla, received 12 years for terrorism. They were found guilty of laying land mines that injured eight people in Transvaal Province in 1986.