When asked "Are you an agnostic or an atheist?", Russell replied:
Agnostic, of course. Atheists are like Christians: That is, both dogmatically mantain that we can know whether or not there is a God. The Christian holds that God does exist; the atheist holds that God does not. But the agnostic knows that we simply do not possess sufficient grounds either to affirm or deny the existennce of a supreme being. So I believe that although the existence of God is not impossible, it is improbable. Quite improbable.

A more clarifying answer, as mentioned above, can be found in Am I An Atheist Or An Agnostic? (1947), where Russell states:


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 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.


Regards,