The Miranda Warning, which protects your rights regarding police interrogation, does not need to be given to you if you are not under arrest. If you are not arrested for a crime, you are not going to go to trial for a crime, so there is no need to give you a Miranda Warning so that what you say can be used against you at trial.
This is why on popular television shows the police are sometimes shown speaking to a person for some time before they read them their Miranda Rights. They have reached a point where they feel the suspect is beginning to incriminate himself or herself, and they are protecting the suspect’s rights and protecting their own ability to use the person’s testimony at trial by reading the Miranda Warning. Television gets these things right sometimes!
You will not be arrested for politely declining to answer questions, but a situation that requires police intervention is unlikely to be simplistic enough for that response. Police could arrest you for many other reasons, including ‘probable cause,’ so always be polite and do not aggravate the situation.
If you have been Mirandized and you waive your rights, meaning you wish to speak to police freely without an attorney present, you can change your mind at any time and ‘plead the fifth,’ meaning you no longer wish to answer questions, or that you have changed your mind and wish to have an attorney present after all.
If you have concerns that you may incriminate yourself by speaking freely to a police officer, by all means request that your attorney be present.