I have not been arrested, but I am supposed to go in for questioning. Should I ask if I am under arrest and keep my mouth shut until I have an attorney or public defender?

First, no one has to answer questions by the police (other than providing their name and producing identification if the police stop them). Just because the police tell you they want you to "go in for questioning" does not mean you have to do so. You have every right to refuse to speak with the police. And you should, unless you have first consulted with a lawyer who has advised you differently and who is present when you speak with them. It is important enough to repeat: If you are going to speak with the police, you should do so with counsel. The police will give you "Miranda" warnings, and they mean it: Anything (and everything) you say can (and likely will) be used against you in court. The jails are filled with people who thought if they could only explain things to the police, they wouldn't be charged with a crime. Unfortunately, with very few exceptions, if you have not been charged with a crime, you are not entitled to have the public defender appointed to represent you. The right to appointed counsel does not attach prior to the beginning of legal proceedings against you--usually considered to be the filing of charges. If you voluntarily appear at the police station for questioning, it is not an arrest. You are only considered to be "under arrest" if you are not free to leave--if your freedom of movement has been restricted in any significant way. If at all possible, you should retain the services of an experienced criminal defense attorney in your area and have them contact the authorities who want to question you. After speaking with you and with the police, your lawyer can best advise you as to whether you should speak with them.