I have an expired US passport, and due to an family emergency in America, i need to travel immediately. The US embassy where i live cannot renew my passport for another 2-3 weeks. I have dual citizenship. Can i use my foreign passport to obtain ESTA and enter into the US? I have already applied for the ESTA, and stated that i also have a US passport. It has been approved. Will i still have a problem entering?
Technically, you cannot be denied immigration into the U.S. because you are a U.S. citizen. Your expired passport is a good proof of that. You can just use your valid foreign passport for leaving the country. The worst thing can happen to you is just some questioning by officials upon entry - once they established your identity and the status of a U.S. citizen, they must let you enter.
There is a legal and a practical side to this question:
Legal: As a dual citizen you are required to enter the US with your US passport. Since you are a US citizen you can't be denied entry in the US.
Practical: While you can't be denied entry, the powers at be can make it as miserable as they feel like. At best its a couple of hours at secondary inspection, at the worst it could be multiple days and massive legal bills.
Furthermore, you need to get to the border first. No airline will let you board with an expired passport and according to their contract of carriage, they have every right to deny you boarding.
The ESTA application process asks you specifically if you have ever been issued a passport from a different country and whether you have other citizenship. If you answer truthfully, you will not get ESTA since you are a US citizen. You'd have to lie on the application, which isn't a great idea.
So in order to use ESTA you have to violate at least two current laws. However, there isn't high priority enforcement on these, so it's unclear what your chances of getting caught are and what the consequences of getting caught would be.
Conclusion: It would be by far the safest and most legal course of action to have your US passport renewed as quickly as possible. Usually embassy and consulates are happy to expedite if you pay the fast track fees.