The defunct processes are the remains of processes whose parent hasn't called wait(3) on yet - they are not consuming any resources other than slots in the process table. A web server that is under high load might be spending more time processing new requests than waiting for it's children (your CGI programs). This can be further compounded if you are using a database engine that will spawn new processes as children of your CGI program for instance.

I would throw the ball back in the court of the administrator of the server as it is probable that the servers hardware is not coping with the number of requests that is being asked of it.

/J\