South African police reported that seven blacks were killed in riots on the eve of the promised lifting of the country's partial state of emergency. President Pieter W. Botha said earlier that he would probably end the state of emergency today in 23 districts after what he called a decline of violence. Fire heavily damaged the Johannesburg office of the Release Mandela Committee, which has worked for the release of black nationalist leader Nelson Mandela. Aubrey Mokoena, the group's publicity secretary, blamed police for the fire. Police denied it and arrested him on an unrelated charge.