1. Ask "Am I under arrest?" 2. If the answer is anything other than "Yes" ask "Can I leave now?" 3. If the answer is anything other than "No," get up and leave! Don't ask for permission, don't say another word. Just leave. If anyone tries to stop you, say "Unless I am under arrest, I am going to leave NOW. If you prevent me from leaving than I am assuming I am under arrest. If so, please read me my miranda rights right now."
If they read you your rights, ask for a lawyer. Specifically say "I want to speak to a lawyer and I chose to remain silent and not answer any questions until I speak to a lawyer." If the cop tells you that your lawyer is on his/her way and then continues to talk to you, you should say "I see you continue to talk to me, I am going to assume that you are trying to elicit statements from me after I invoked my rights. I am going to relay this information to my lawyer."
If you are innocent, you have NOTHING to gain from talking to a cop. If you are guilty, you WILL hurt your case every time.
UPDATE: Spelling