The Senate Foreign Relations Committee postponed a scheduled vote on President Reagan's $350 million Caribbean aid initiative because the Defense Department has not turned over a report on El Salvador. An aide said the Pentagon report deals with El Salvador's future needs for US military aid and advisers. About one-third of the proposed Caribbean aid would go to El Salvador.
Both the Senate committee and a House of Representatives foreign affairs subcommittee have demanded to see the report on El Salvador before a vote is taken. But Assistant Defense Secretary Francis West told the House subcommittee last week the report ''is an internal working document,'' suggesting that Congress therefore could not see it.