U.N. Secretary General Javier Perez de Cuellar will issue a new report on the U.S. threat to close the Palestine Liberation Organization's U.N. mission, his spokesman said. He said the report will be issued before the General Assembly resumes on Monday, expressly to debate action approved by Congress to terminate the mission by March 21. In an earlier report, Perez de Cuellar proposed arbitration. Diplomats believe the General Assembly will probably choose to refer the matter to the World Court for an advisory opinion. The PLO has had a U.N. mission for about 13 years with observer status.