[Laitoste]

It depends on what you mean by symbolism. Naturally, you have items that are meaningful and symbolic for characters, such as Anduril for Aragorn, but if you want to read in any more than that, you are treading dangerously close to allegory. And, as we all know, Tolkien "cordially dislike(s) allegory in all its manifestations."

On the other hand, some elements are strikingly similar to stories/myths in our world. It is difficult to NOT see these elements (like the similarity of Eru to God) while reading. However, most of the time, Tolkien's stories do accomplish "applicability."

Now, to answer your question, Glirdan, it would be difficult to see Gandalf as God. Perhaps he could be seen as a god-like figure, or a Christ-figure, as has been done before, but he does not have enough of God's qualities to be any sort of representation. However, to a certain extent, he does represent Eru in Middle-Earth. It would probably be more accurate to say he represents the Valar. If you so wish, you could see this as a more symbolic representation, but contextually, he really is a representative of the Valar and Eru.

Sauron, on the other hand, may represent Morgoth on a symbolic level, but not on a literal level. Morgoth did not elect Sauron to go to Middle-Earth and wreck havoc on Morgoth's behalf. Personally, I don't know enough about the Devil to proclaim Sauron's resemblance. I don't even know if I believe there is an evil entity known as the Devil yet. Anyway, if you wanted to read Sauron as a symbolic representation of Morgoth, it wouldn't be much of a stretch, but you may lose something in the reading. Such is the problem with allegory and symbolism. You begin to read everything as representing something else, and forget to appreciate the story for simply existing.