@:Rogerio: I believe the OP wants to filter the number of rows returned by a query, based on user input. Passing a parameter would only work if the table contains a row number object exposed to the universe, which is of course a viable option if this criteria is satisfied.
@OP: You can use the database ranking function in the query designer (if your DB supports it) to achieve this, but this is going to effect a ranking - not strictly speaking just returning 'n' rows - and you'll need a measure object in the query for a ranking basis.
There's probably numerous ways to do this at the Universe / semantic layer level; if you want to do this just at the report level, I think you'll struggle.
HTH
NMG