Depends on which implementation you are using. On G95 (taken from the G77 manual), it has
10.11.9.133 IArgC Intrinsic
IArgC()
IArgC: INTEGER(KIND=1) function.
Intrinsic groups: unix.
Description:
Returns the number of command-line arguments.
This count does not include the specification of the program name itself.
10.11.9.118 GetArg Intrinsic
CALL GetArg(Pos, Value)
Pos: INTEGER; scalar; INTENT(IN).
Value: CHARACTER; scalar; INTENT(OUT).
Intrinsic groups: unix.
Description:
Sets Value to the Pos-th command-line argument (or to all blanks if there are fewer than Value command-line arguments); CALL GETARG(0, value) sets value to the name of the program (on systems that support this feature).