can you tell me i am in usa and i want to applied for australian pr but can u tell me police clearance certificate is how log valid for australiya for process thanks pl help me i am going india next month
It is normal practice for immigration to advise applicants to get health and police checks done after immi have done an initial examination of an application.
Before you put in an application, I'd suggest you familiarise yourself with current applications prioritisation for processing - have a look at sticky thread #4.
Existing applicants are being advised if they are not in a priority situation that it is expected their application would not even be considered in the 2009-2010 financial year.
If global/Australian economics do not improve, I'd think that situation would continue for following years.
Some people front load their overseas police clearances at the start of the application to save time in processing. but these days, with delays in non priority categories, you might have to do them twice if you front load them.