To define a record sequential file with variable length records:
file control. select recseqv assign to "recseqv.dat" organization is record sequential. ... file section. fd recseqv record varying from 3 to 80 characters depending on ws-record-length. 01 recseqv-fd-record pic x(80). ... working-storage section. 01 ws-record-length pic 99.
You could simply use ORGANIZATION IS SEQUENTIAL, as record sequential is the default for sequential files, as long as the SEQUENTIAL Compiler directive is not set.