Pope Benedict XVI asked pilgrims who gathered Sunday in St. Peter's Square in the Vatican to pray for the success of his trip this week to the United States.

He said he wants the six-day visit, his first to the U.S. since being chosen as leader of the Roman Catholic Church on April 19, 2005, to be a "time for spiritual renewal for all Americans."

The Pope's trip will begin on Tuesday with a stop in Washington, D.C., where he will visit the White House the following day. On Thursday, he'll speak to educators at the Catholic University of America and meet with multi-faith leaders at the nearby Pope John Paul II Cultural Center.

The pontiff will then travel to New York City on Friday for a speech to the United Nations, which will coincide with the UN's marking the 60th anniversary of its Universal Declaration of Human Rights.

He will visit Ground Zero in lower Manhattan next Sunday, April 20, the last day of his tour.

When he arrives at the White House, one of the men greeting him will be Rev. Thomas Rosica of Toronto, who said the style of this visit will differ from those of Benedict's predecessor.

"It's a very symbolic visit. These are not the great crowd scenes and the multi-city visits of Pope John Paul II, who was young when he first came in 1979. This is an 80-year-old. In fact, he'll be 81 years old at the White House on Wednesday, his birthday," Rosica told CBC on Sunday.

Rosica said the Pope would be speaking about world peace during his U.S. visit and "perhaps encouraging nations to choose other means to settle differences and difficulties rather than war."

"So it's a very, very appropriate moment because the world as we know is torn apart right now by many different wars," he said.

Rosica, who is chief executive officer of the Salt and Light Catholic Media foundation and Television Network in Canada, said the preparations for the visit have been "remarkable."

"It's a massive security effort. Thank God we didn't have these security worries in Toronto in 2002 [during Pope John Paul II's visit], but because of the recent statements by bin Laden and other terrorist organizations, I think the security will be at a very high degree."
 
Last month, an audio message attributed to al-Qaeda leader Osama bin Laden accused the German-born Pope of leading a "new crusade" against Muslims.

Al-Qaeda and its supporters have issued several threats against the Pope since he quoted a medieval Byzantine emperor in a speech in Germany two years ago referring to some of the teachings of the Prophet Muhammad as "evil and inhuman."

The Pope apologized for the anger caused by the speech, saying that the view expressed in the quotation was not his own.