Yes, a reader finds the exact passage I had in mind in probably my favorite essay by Buckley. From a reader:

In one essay, Buckley responds to Max Eastman, who had resigned from NR due to his discomfort with its stand on religion and politics. Eastman was an evangelistic atheist of the old school (like Robert Ingersoll et al).
See “Notes toward an empirical definition of conservatism” section IV, where Buckley says:
“Can you be a conservative and believe in God? Obviously. Can you be a conservative and not believe in God? This is an empirical essay, and so the answer is as obviously, yes. Can you be a conservative and despise God, and feel contempt for those who believe in Him? I would say no.”