This is an old debate. One side says that America was founded upon Christian principles. Another says that the founding fathers were not Christian at all. Well, a new article in The Nation (Thanks Vince) brings up a nice primary source to address the issue. From the 1797 Treaty of Tripoli:
"As the Government of the United States...is not in any sense founded on the Christian religion--as it has in itself no character of enmity against the laws, religion, or tranquility of Musselmen--and as the said States never have entered into any war or act of hostility against any Mehomitan nation, it is declared by the parties that no pretext arising from religious opinions shall ever produce an interruption of the harmony existing between the two countries."
This was signed by President Adams, and ratified by a unanimous vote in the Senate. While this was the 339th recorded vote in the Senate, it was only the third unanimous vote. There was no debate over the wording.
That should make things pretty clear.
Jefferson, Franklin, Paine... the most clear-cut deists and atheists, and also the people who really laid the remarkable framework of our nation. This seems to set up a pretty interesting trend: The more you base your life on the mistranslated words of a probably-fictional Jewish carpenter who supposedly regurgitated a bunch of common sense, interspersed with psilocybin-induced hallucinations some 2000 years ago, the less likely you are to do anything good in government.