I'll take a whack at my own question here, based on the comments and additional resources folks have pointed out.
It appears that there is not an "agreed upon" definition of agnosticism (and to a lesser extent, atheism), even from a more narrow or formal philosophical perspective for the purpose of understanding one's epistemological position. Even so, there does appear to be commentary in the literature where attempts are made to create this distinction.
The weak, soft or "man on the street" form
Russell Bertrand does equivocate between agnosticism and atheism, stating that he would tell a philosopher that he is an agnostic, while telling a "man on the street" that he was an atheist, as discussed here.
As a philosopher, if I were speaking to a purely philosophic audience I should say that I ought to describe myself as an Agnostic, because I do not think that there is a conclusive argument by which one can prove that there is not a God. On the other hand, if I am to convey the right impression to the ordinary man in the street I think that I ought to say that I am an Atheist, because, when I say that I cannot prove that there is not a God, I ought to add equally that I cannot prove that there are not the Homeric gods.”
― Bertrand Russell, in Am I An Atheist Or An Agnostic? A Plea For Tolerance In The Face Of New Dogmas (1947 or 1949)
This does appear to get at the general problem with these two terms. There are "hard" and "soft" forms of both, and sometimes the formulation for what is "hard" and what is "soft" (or strong and weak) overlap each other, depending on who is creating the formulation.
For example, one can use the term agnostic to simply indicate that one doesn't have enough information to make a decision yet. This is the "common" definition (or "man on the street" version). In this sense, it typically also implies that one feels no urgency to make a decision and/or is not urgently seeking more information. In this sense, one can be agnostic about just about any subject - you could be agnostic about theism, or atheism, about the origin of the universe (in either case), or practically about any worldview or philosophical framework.
If you state you are an agnostic according to this "common" definition, the proper follow-up question is "agnostic to what?" Are you agnostic to theism, or agnostic to atheism, or agnostic to both, or agnostic to any philosophy at all?
The strong, hard and/or philosophical form
Bertrand seems to imply there is a more philosophical form of the term(s), or at least one which a philosopher will understand, while a "man on the street" will not. By this he must imply that a philosopher would naturally put an agnostic in the atheism camp, and he is first an atheist, believing there is not a God, and secondarily, agnostic, in that in some sense he is either open to further evidence, or simply believes on an epistemological level that it is not possible to prove the non-existence of God.
I consider the strong form of agnosticism to go even a step beyond Russell's position. A "strong form" agnostic doesn't make a final decision on whether God exists or not. They believe that there is not enough evidence to prove the case either way (pro or con). T.H. Huxley's position is described this way in Atheism and Agnosticism (Standford Encyclopdia of Philosophy)
Huxley thought that we would never be able to know about the ultimate origin and causes of the universe. Thus he seems to have been more like a Kantian believer in unknowable noumena than like a Vienna Circle proponent of the view that talk of God is not even meaningful. Perhaps such a logical positivist should be classified as neither a theist nor an atheist, but her view would be just as objectionable to a theist. ‘Agnostic’ is more contextual than is ‘atheist’, as it can be used in a non-theological way, as when a cosmologist might say that she is agnostic about string theory, neither believing nor disbelieving it. In this article I confine myself to the use of ‘agnostic’ in a theological context.
Huxley's agnosticism seems nevertheless to go with an extreme empiricism, nearer to Mill's methods of induction than to recent discussions of the hypothetico-deductive and partly holistic aspect of testing of theories.
... Huxley thought that propositions about the transcendent, though possibly meaningful, were empirically untestable.
Note that part in the middle about the Vienna Circle that believes talk of God is not even meaningful is called Ignosticism