BRASILIA, May 31 (Reuters) - Brazil’s government debt as a share of gross domestic product fell sharply in April to 86.7% from 88.9% in March and the public sector posted a primary surplus of 24.3 billion reais ($4.7 bln), the central bank said on Monday. The public sector surplus excluding interest payments was much more than the 16.75 billion reais forecast in a Reuters poll of economists, and the overall deficit in the 12 months through April shrank to 7.1% of GDP from 9.1%. $1 = 5.22 reais Reporting by Jamie McGeever; Editing by Alison Williams Our Standards: The Thomson Reuters Trust Principles.