Agnosticism is more about the knowledge. Atheism is about the belief or lack there of. Both theist and theist can be agnostics.
Gnostic theist - i know and believe there is a god.
Agnostic theist - i dont know if there is a god but i believe there is one
Gnostic atheist - i know there is no god and and i dont believe in one
Agnostic atheist - i dont know if there is a god and i dont believe there is one