If it is 11g then you may give, just check the option for multiple values. provided, you convert the filter to SQL.
Let me know for issues.
Mark if helps
Edited by: Srini VEERAVALLI on Feb 6, 2013 7:54 PM
Multiple default values for a presentation variable is only possible in 11g as Srini Said.
Check mark : Enable user to select multiple values. (under variable datatypes)
If it is 10g, then it is not possible.