I have no doubt Morris believes that quote, but I agree that he may not have said those specific words.
Bush, this page (
http://www.skeptictank.org/gbush.htm) gives some info, although it doesn't give any more support for that specific quote, it does support the attitude.
"C. Boyden Gray, counsel to the president, reply on White House stationery on February 21, 1989, stating that substantively Bush stood by his original statement.
"As you are aware, the President is a religious man who neither supports atheism nor believes that atheism should be unnecessarily encouraged or supported by the government."
That site was funny, but they really really really should have cited sources.