Если сценарий может работать под Администратором, он может использовать команду wmi.
FOR /f "tokens=2 delims==" %%f IN ('wmic os get osarchitecture /value ^| find "="') DO SET "OS_ARCH=%%f"
IF "%OS_ARCH%"=="32-bit" GOTO :32bit
IF "%OS_ARCH%"=="64-bit" GOTO :64bit
ECHO OS Architecture %OS_ARCH% is not supported!
EXIT 1
:32bit
ECHO "32 bit Operating System"
GOTO :SUCCESS
:64bit
ECHO "64 bit Operating System"
GOTO :SUCCESS
:SUCCESS
EXIT 0