My SSRS report contains 7 input parameters and while running my report the size of the parameter(i.e. length) is increasing.
One of my input parameter(drop down list
This doesn't help the OP with SSRS-2008 but in case it helps others - Microsoft have improved this in SSRS 2016 - parameters can now be easily managed via the GUI in Report Builder / Visual studio:
https://www.intertech.com/ssrs-parameters-2016-update/