What degree of authority does the Pope hold to reveal and declare doctrine, or the word of God?

When Jesus was on the Earth, He (obviously) held the authority to declare whatever doctrine he wished, as the ultimate authority in His church. On a tier just below that, prophets like Moses were granted authority to essentially act as God's voice on Earth. To the people following them, there was no functional difference between receiving a commandment from one of these prophets, and from God's actual voice. Exodus 4:16 is an example of principle: > And he shall be thy spokesman unto the people: and he shall be, even he shall be to thee instead of a mouth, and thou shalt be to him instead of God. I am a member of the Church of Jesus Christ of Latter-Day Saints, so I am accustomed to the idea of having a prophet now who still receives revelation from God in the Isaiah or Moses archetype. I can also comprehend fairly easily, after discussing with my Protestant friends, the concepts and practice when one believes in the end of such a tradition, and relies on the scriptures and personal conscience instead. What I'm fuzzy on is what happens in what feels like a blurry middle ground--where one still believes in following a single leader, who has been ordained by God to lead His church, but one does *not* go so far as to give him the same authority as Moses/Elijah/Peter and the like. Does the Pope have power to announce "thus saith the Lord" and pronounce new scripture? To clarify existing doctrines, but not give new (to us) ones? To give definitive interpretations of scripture?