I thought an agnostic is someone who is not sure whether or not G-d exists, as opposed to an atheist who thinks he is sure that kaviyachol, I don’t want to even say the words, but you get the idea.
That is why many say that there can’t really be such a thing as an atheist because no one can say that he knows for sure such a thing (especially since “ther is no atheist in a fox hole”), so people who call themselves atheists are really agnostic.