If Ronald Reagan should oust Jimmy Carter from the White House, the country's most famous born-again Christian Sunday School teacher will be replaced by another born-again Christain who was once a Sunday School teacher.

One insider told my associate Dale Van Atta, "Reagan is religious the way a lot of Americans are. He goes to church several times a year -- on the holidays. He just doesn't feel it's necessary to go every Sunday."

In answer to a questioner on the campaign trail, Reagan allowed that, while he might not pray every day, he prayed enough so that "the 'Man upstairs' must get pretty tired of hearing me." It was a deft answer, with a sly needle for Jimmy Carter, who boasts that he prays several times a day.

Ever since George Washington took the oath of office with his right hand on a Bible, a belief in God has been pretty much taken for granted in American presidents. And except in 1928, when Al Smith's Catholocism was an issue, and in 1960, when John Kennedy laid it to rest, a presidential candidate's religion -- or lack of it -- has had little effect on his success either as candidate or as president.

The historical record shows that, while there have been no atheists in the White House, the degree of religious fervor among those who have run for president has varied widely.

The most passionately religious candidate -- at least until Jimmy Carter came along -- was Williams Jennings Bryan, a fundamentalist who was rejected by the voters in all three tries for the presidency. On the other hand, the man whom historians regard as the most deeply religious of any president, Abraham Lincoln, was one of two chief executives who never belonged to an organized church, (The other was his immediate successor, Andrew Johnson.)

Asked once if he was a "born-again Christian," Reagan replied in the affirmative, but without elaboration. Associates say he meant to get across the idea that he had not undergone the dramatic inspirational conversion that Carter did at the age of 42.

Officially, Reagan lists his religiious persuasion as the Christian Church (Disciples of Christ), a sect of about 800,000 members that grew up along the Middle Border in the last century. His mother, Nelle, described by her son as a "natural, practical do-gooder," enrolled him in the church and he graduated from its college, Eureka, in Illinois.

But Reagan is not a "practicing disciple" like his mother, and hasn't attended the denomination's servics for some time. The First Christian Church of Sacramento invited him to attend when he became governor of California, but he never took it up on it.

Instead, he and his wife Nancy favored the Bel Air Presbyterian Church, because the pastor, Rev. Donn Moomaw, was a personal friend. Reagan consulted Moomaw for spiritual guidance on occasion while he was governor.

Aside from Reagan's stand against abortion, the only discernible reflection of religion in his political views is a statement he made in a television speech in the 1976 campaign: "Call it mysticism if you will, but I believe God has a divine purpose in placing this land between the two great oceans, to be found by those who had a special love of freedom."

Interestingly, this happens to be a tenet of the Mormon faith, and one of Reagan's closest advisers, Richard Wirthlin, is a devout Mormon.