In order to switch the kernel boot mode in Mac OS X permanently you will be need to perform this at the command line.
In order to determine the current kernal boot architecture setting run the following:
systemsetup -getkernelbootarchitecturesetting
In order to set the kernel boot architecture run the following:
sudo systemsetup -setkernelbootarchitecture i386 | x86_64 | default
For example, to set the kernel boot architecture to 64-bit mode run the following command:
sudo systemsetup -setkernelbootarchitecture x86_64
If you require to temporarily set the kernel boot architecture at start-up, you can do this be pressing “3+2” for the 32-bit mode and “6+4” for 64-bit mode when powering on.
Deans Blog 
it says it is set to default???
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