You may apply for "Re-entry

Permit". It allows you to stay outside US for more than 6 months without worry having trouble to return the US. Go to www.cis.gov to get form I-131. Follow the instruction where to file. Re-entry Permit is valid for 2 years. You must return the US within 2 years. Then you can re-apply again. "Re-entry Permit" is only good for you when you stay outside of US more than 6 months. But you still have the prolem when you apply for naturalization. If you stay outside US more than 6 months, it cuts your continuing reside in the US and the time in the US will be re-account (start again) after you come back. So you can not apply for naturalization if the total time in the US is less than 5 years.