the police can use "observation" as a basis for public drunkeness. And that's a fact.
a cop can arrest you anytime he/she pleases, really. Never resist arrest, it turns into a class 6 felony. A cop does not even have to say you are under arrest, the cop need only make the gestures.
Your remedy is, take it to the judge. For the record, they don't have to Mirandize you because you were arrested. Criteria for Miranda: you must be in a custododial setting and the police are planning to use what you say against you in a court of law.
that's what I learned in criminal procedure and criminal trial procedure.
good luck.