What will happen if I present an expired Green Card when I try to reenter the United States after traveling abroad, or when I obtain a new job, or when I apply for entitlement benefits?
Re-entry into the United States from abroad: To the extent possible, apply for your new Green Card before you travel and bring with you on any trip the temporary documentation you receive at the time of filing to renew your Green Card. If after traveling abroad you try to re-enter the United States with an expired Green Card, you may experience a delay during the inspection process at the port-of-entry.
http://www.foreignborn.com/visas_imm...reen_cards.htm