The U. S. Constitution’s lack of a Christian designation had little to do with a radical secular agenda. Indeed, it had little to do with religion at all. The Constitution was silent on the subject of God and religion because there was a consensus that, despite the framer’s personal beliefs, religion was a matter best left to the individual citizens and their respective state governments (and most states in the founding era retained some form of religious establishment). The Constitution, in short, can be fairly characterized as “godless” or secular only insofar as it deferred to the states on all matters regarding religion and devotion to God. http://wallbuilders.com/LIBissuesArticles.asp?id=84
Furthermore, the Constitution was signed “In The Year of our Lord”; notice they chose the word “our” to reference their faith in the Lord Jesus Christ.
Other evidence of the faith of our Presidents was how they signed presidential documents. Even Thomas Jefferson, the one coined for the term “Separation of Church and State”, signed his presidential document as “in the year of our Lord Christ”. President Adams, James Madison, George Washington signed documents in the same format. They had Jesus Christ in the center of what they did and it was understood that Judeo-Christian principles was at the center of American culture and government.