exodus - Our Founding Fathers were libertarian, and I don't think anyone would ever accuse them of being atheists.
All I've read about deists says that even if they weren't mainstream Christians, they certainly weren't atheists. They believed in God.
Ben Franklin called himself a Christian, but he noted that he had serious problems accepting that Jesus and God were the same person. I share his skepticism on that point, but I am a Christian just the same.
My requirement for the title "libertarian" is a belief in the Rights of Men, and in the Rule of Law. Our Founders qualify.