"Officer" for the most part in the USA. Unless it's a Sheriff's Deputy, some get upset when they are called "Officer". Texas Rangers want to be called "Ranger". Massachusetts State Police want to be called "Trooper" (and don't you forget it!). "Sir" and "Yes Sir" will keep you from "falling down" if you get into trouble.

Here's an article from The Moscow Times:

Good Cop, Bad Cop 03 March 2011
By Michele A. Berdy
Полицейский: police officer
Пришла весна и народ гуляет! (Spring is here, and folks are having fun!) Or: Ещё не пришла весна и народ с ума сходит! (Spring still isn’t here and folks are going nuts!) In any case, ребрендинг (rebranding) of милиция (militia) into полиция (police) has been народное творчество (public creativity) of the best kind. Reading the news is like a night at a comedy club.
It all started with an article on how the public should address the newly named cops. A language expert admitted that he didn’t have any idea. Theoretically, we should politely call a cop господин полицейский (Mr. Policeman), but he said: Статус нашей бывшей милиции, а теперь полиции как-то очень плохо вяжется со статусом слова “господин” (The status of our former militia and now police for some reason really doesn’t fit the status implied by the word “mister”).