John_Ryan is correct: the processor is little endian. However, if you are using this information to decide whether to "increment or decrement the pointer" to the integer you may be surprised at the result. Incrementing an integer pointer will not generate a pointer to the high-order byte, but to the next integer instead. (You may know all this already for all I know.) It might be a good idea to just use this technique, which will work with any "endianness":
//writes myint to EEPROM at offset 0/1
EEPROM.write(myint % 256, 0);
EEPROM.write(myint / 256, 1);
Mikal