The simplest way to do this is to run through all the items of one list and see if they are in the other list:
set originList to {"pear", "banana", "strawberry"}
set superList to {"banana", "pear", "strawberry"}
checkEquivalence(originList, superList)
on checkEquivalence(list1, list2)
-- check if list are the same size; can't be equal if they are not
if (count of list1) ≠ (count of list2) then return false
repeat with thisItem in list1
--check if each item in origList is in superList; set
if thisItem is not in list2 then
return false
end if
end repeat
return true
end checkEquivalence
If you have very large lists this will not be efficient - you'd need to use some optimizing tricks - but for shortish lists this should be fine.
The other way to do it would be to sort the two lists and compare them directly. This is more difficult: either you have to implement an applescript sort routine (there are efficient ones on the web if you google, but they are hard to wrap your head around unless you're an applescript pro), or you have to download and install the Satimage osax and use its sort routines.