How about: "My lawyer would be happy to answer all your questions".
Is that enough? Or does one need to explicitly add "I am invoking my rights under the fifth amendment"? Or explicitly state that "I want a lawyer" (which, doesn't make sense for a person who already has too many lawyers).
I'm looking for one polite, simple, clear statement to use.
While "My lawyer would be happy to answer all your questions" could be sufficient, why leave it to chance? Just be very clear since the situation could result in life-changing consequences: "I am invoking my right to remain silent and will only answer questions with a lawyer present."
Edit: stop worrying about winning the hearts of police in a situation like this. Their interests are diametrically opposed to yours at that point in time. No need to be an asshole but you're also not going to hurt their feelings by protecting your interests; and if they seem to take issue with your statement (social pressure is another interrogation tactic, BTW), just remember that this is not a social situation so their opinion of you is not relevant. Investigators are not going to lay off you just because they think you're a swell person.
> YOUR magic words: "I'm not answering any question and I want a lawyer"
then shut the fuck up.
Although I think you have to provide your identity to officers? Not sure.
I heard a story about Larry Ellison pulled over by the police in the parking lot of Oracle. Apparently he said "Call my lawyer", handed them his lawyer's card, and walked into the building.
There is another reason to use the recommended phrase, too: it's a standard. More people will immediately understand your intent (regardless of how they respond).
> I want to be polite
While general politeness is always a good idea, the police are not on your side and you absolutely should not go out of your way to appease them. If they want to hassle you, they are going to do it anyway. In practice, they probably already made their quick-and-arbitrary conclusion before they started talking to you.
Don't take my word for it - this is the advice any decent lawyer will give you. I highly recommend watching this[1] lawyer explain the public<->police interaction, corroborated by a police officer who explains how they try to scam you into talking.
[1] https://www.youtube.com/watch?v=6wXkI4t7nuc
edit: fixed minor editing error