I don't think he was atheist though it appears he don't give crap for religion.
Perhaps based on the God song he wrote, he believed in love, running around lush gardens stark nekkid, tossing flowers in the air and hugging trees.
Tsk tsk tsk... a real romantic (i wonder which sign he born under).
God is a concept
By which we measure
Our pain
I don't believe in magic...
I don't believe in Bible...
I don't believe in Jesus...
I don't believe in Buddha...
I just believe in me
Yoko and me
And that's reality
"I'm not afraid of death because I don't believe in it. It's just getting out of one car, and into another."
- lennon