Is it considered in good form to offer a draw when you are down a pawn? I am playing a correspondence game that I think is a drawn rook ending. I am down a pawn and would like to offer a draw I have had similar situations at chess.com.  

Well if you think it is draw you might wait a bit and make sure it is I'd say. If you're not sure yourself then your opponent might not be sure or know it's winning.

I'd just play some more I guess.

It's fine to offer a draw if you think you have a drawn position, even if you're behind on material.  Even down slightly in an unclear position is still reasonable, IMO.

Where it gets to be poor form is when you're losing badly, and doing it just to be a nuisance, or (even worse) hoping that your opponent will accept it by accident.  VERY poor form.

As Tarrash said: "All rook endings are drawn", so I think it's OK to offer a draw in your case. 

I do not think it is in bad form to offer a draw when down by just a pawn - especially in a game that appears to be headed toward a drawn rook ending anyway. As was mentioned by Spiffe, it is in bad form to offer a draw when losing badly or to simply be a nuisance.

You have nothing to lose by offering a draw. Remember, it is no more than an offer. Your opponent has the option to either accept or decline your offer.

I agree, offering a draw is a right of the game.  It isn't an insult or bad form, I enjoy draw offers when I'm about to checkmate the person, it amuses me and you never know your opponent may be willing to take the draw whether he's up or not.  Wins are never guaranteed no matter how substantial the advantage may appear.  I have no problem with draws if i think the game was a good enough game and close enough to draw.