IT sounds like you are hoping from some sort of SQLish "top" clause to stick inside your WHERE.
Rule #1 -- Progress is not SQL.
Rule #2 -- The harder you try to make Progress into SQL the unhappier you will be.
If you are using FOR EACH logic then just do as Cringer says and insert a counter.
If you are using a QUERY you might want to show that code instead of an example with FOR EACH but you might also find the CACHE option interesting if you're trying to limit the size of the result set. I.e.
DEFINE { [ [ NEW ] SHARED ] | [ PRIVATE | PROTECTED ] [ STATIC ] }
QUERY query
FOR buffer-name [ field-list ] [ , buffer-name [ field-list ] ] ...
[ CACHE n ]