"He (the Pope) really does have a European's outlook on the world. And that of course is quite different from the way the Bush administration looks at the world," Schneck said.
The affable Bush sets great store in personal relationships and distrusts academics while the German-born Benedict, a theoretician and theologian, rose through church ranks on the basis of his intellectual brilliance.
"The Pope is somebody who came through the ranks in an institution that is very hierarchical, very structured, very legalistically oriented," Schneck said. "And so he's an institution man and therefore tends to give deference to procedures by which institutions operate."
"In contrast, I think President Bush prefers a more personal approach, he likes the direct one-on-one, mano-a-mano kind of approach."
Bush, a Methodist, and the Pope both oppose abortion, euthanasia and embryonic stem cell research. But they differ on the death penalty, which Bush supports while the Catholic Church opposes in almost all cases.
Pope Benedict recently praised "the American people's historic appreciation of the role of religion in shaping public discourse and in shedding light on the inherent moral dimension of social issues".
Regardless of their differences, the United States must maintain a relationship with the Vatican, said John Green of the Pew Forum on Religion and Public Life.
"The United States and the Roman Catholic Church have to deal with each other, whether they see eye-to-eye or not," he said. "This kind of meeting presents an opportunity for these leaders to get to know each other, to talk about things, maybe to say some things to each other that they wouldn't want to say publicly."
The two met for the first time last June at the Vatican and discussed the Middle East, aid to Africa and the Iraq war.
Bush greets Pope Benedict at Andrews Air Force Base on his arrival on Tuesday and will hold a special South Lawn ceremony, a private Oval Office meeting, and then a dinner for the pontiff at the White House on Wednesday, which happens to be the Pope's 81st birthday.
