Although records are transferred from the Department of State to the National Archives on a regular schedule, it takes time to process newly transferred records and make them available for researchers. Department of State records from the late 1970s and early 1980s are likely at the National Archives but may not yet be available for researchers.The best guide to what's available is the Archival Research Catalog (ARC). Search ARC using keywords and dates to determine whether there are any records available on your topic. Note that most records are not available online.
See U.S. Department of State, Freedom of Information Act under Records Management for detailed explanations about how the records from various Department of State offices are handled. In general, records are transferred to the National Archives after 25-30 years.
U.S. Department of State Information Access Guide outlines the process of placing a Freedom of Information Act (FOIA) request for the declassification of documents.