The Nicaraguan government is withholding approval of the names the State Department has submitted as replacements for eight U.S. envoys who were expelled by Sandinista authorities last month, a spokesman said Friday. Other officials said the administration does not intend to replace Ambassador Richard Melton, who was among those expelled, but instead plans to send Kenneth Skoug, head of the State Department's office of Cuban affairs, to run the embassy. As embassy charge d'affairs, Skoug would not require Senate confirmation. The officials, speaking only on condition they not be named, said it was doubtful that any ambassadorial nominee could receive Senate confirmation before congressional adjournment on Oct. 8. They said Sandinista refusal to approve the envoys proposed as replacements apparently was in retaliation for the U.S. expulsion of Nicaraguan Ambassador Carlos Tunnermann, who served as chief envoy to both the United States and the Organization of American States. Nicaragua maintains that the administration acted beyond its authority in expelling a diplomat accredited to the OAS. State Department spokesman Charles Redman said a U.S.-Nicaraguan agreement calls for a reply to be given on visa applications for diplomats assigned to either country's embassy within five days of the visa request. The Nicaraguan Foreign Ministry informed the U.S. Embassy in Managua that this provision of the agreement had been suspended and that both the agreement and the U.S. visa requests were under review, Redman said. ``Stalling on the issuance of visas indicates the Sandinista regime wishes to prevent the U.S. Embassy from functioning normally,'' Redman said. On July 11, Nicaragua ordered the seven American diplomats to leave the country within 72 hours, charging that they had been interfering in Nicaragua's internal affairs by encouraging anti-government protests. The State Department denied that the diplomats had acted improperly and ordered Tunnermann and seven of his colleagues home. It said Tunnermann had engaged in unspecified illegal activities during his U.S. stsy and that a U.S. agreement with the OAS permitted the United States to expel any OAS diplomat guilty of such behavior.