You MUST go to the consulate of your home country and get your passport renewed before your adjustment of status interview date. They cannot put a stamp in an expired passport.
This is general information only. It is not intended as a substitute for legal advice, and does not create an attorney-client relationship.
You should try to get a new passport before the interview. It also depends on the officer and what country you are from. I have had officers at the local USCIS office place stamps in expired Mexican passports, but never in any other country's expired passports. Still your safest bet is to get a new passport which you will need anyways.
OK, you need to wait for your interview date. Also, be aware that the Officer will want to see your passport (expired or not), so be careful about mailing it in because you may not get it back in time for your interview. Generally, the Officer wants to see your passport to confirm that you entered legally, etc. It is generally taking less than 1 month to get your green card in the mail. You can mail your passport in right after your interview, while you are waiting for your green card to come in the mail. BTW, this answer is assuming there is no serious emergency that requires immediate travel abroad. You have waited this long, waiting a little longer will be worth it.
Lena Korial-Yonan, Esq.