BRASILIA (Reuters) - Brazil is considering leaving 34 second-tier international organizations, including the United Nations Industrial Development Organization (UNIDO), to cut back on costs, according to a list seen by Reuters.

Brazil has run up $866 million in arrears with international bodies such as the United Nations due to a fiscal crisis, and its diplomats abroad have even had trouble paying their rent, a source with knowledge of the matter said.

The list of possible withdrawals, prepared by the Budget and Planning ministry, includes the Ibero-American summit organization and six institutions in the South American trade bloc, Mercosur.

The source said a decision had not yet been made.

The departure from international organizations would be the latest cost-cutting step by Brazil's new Foreign Minister José Serra, who has vowed to pay the ministry's debts and balance its budget.

Last week 46 ministry positions were closed.

(Reporting by Lisandra Paraguassú; Editing by Toni Reinhold)