Pope Benedict XVI has urged Americans to base their political and social decisions on moral principles, during an 81st birthday visit to the White House.

"I come as a friend, a preacher of the Gospel and one with great respect for this vast pluralistic society," the pope said after he was officially welcomed with pomp, circumstance, a 21-gun salute and a giant birthday cake.

Benedict encouraged US citizens to create a more just society, and called for "patient efforts of international diplomacy to resolve conflicts" and promote progress around the world.

At the outdoor ceremony attended by more than 10,000 people, US President George W Bush wished the Catholic leader many happy returns.

"You've chosen to visit America on your birthday. Well, birthdays are traditionally spent with close friends, so our entire nation is moved and honored that you have decided to share this special day with us," he said.

The president welcomed Benedict to America, citing the role of faith in US life, saying "Here in America, you'll find a nation of prayer."

Cries of 'Antichrist!'

"In a world where some invoke the name of God to justify acts of terror and murder and hate, we need your message that God is love," Mr Bush said. "Embracing this love is the surest way to save man from falling
prey to the teaching of fanaticism and terrorism."

The pope's US trip - the first papal visit to the country in 29 years - has been greeted with a mixture of prayers and protests, as the faithful and those opposing the Catholic church came face to face on the streets of Washington.

Several thousand Roman Catholics from across the US waited for hours, dancing and shaking tamborines, to catch a glimpse of the pope as he left the White House.

"It was in my heart so strong to see the pope, to try to get a blessing," said Carolyn Ehli of Moore, Oklahoma, who clutched a large portrait of the Virgin Mary as she maneuvered her wheelchair to a better viewing spot.

But not everyone came to welcome the pontiff. Roving bullhorn-toting Protestant fundamentalists issued shouts of "Antichrist!" and warned Catholics would end up in hell, while other protesters carried sign accusing the church of harbouring paedophiles.

Ray McIntire, of Parkersburg, West Virginia, was one of a group of burly men carrying banners that equated the Catholic Church with Satan.

Sex abuse scandal

"It's a fake religion," he said. "I believe they worship idols. Every one of these people here to worship the pope today is lost."

As Bush and the pope met nearby, 200 protesters demonstrated over the sexual abuse scandal that rocked the Church, and which the pope said he was "deeply ashamed" of.

Benedict's speech deliberately made no specific references to controversial issues, avoiding anything that could be seen as taking sides in the country's ongoing presidential campaign - apart from saying freedom demanded "reasoned public debate."

The pope and Bush, who spoke privately after the ceremony, oppose abortion and embryonic stem cell research but differ on the Iraq war and capital punishment.

As the pope spoke, the US Supreme Court, led by Bush appointee Chief Justice John Roberts, issued a ruling that cleared the way for executions to resume for the first time since September.

Religious roots

Instead, Benedict concentrated on America's religious roots, which he said were a driving force in a process that "forged the soul of the nation" and won world admiration.

It was Mr Bush who referred to abortion, a hot-button issue particularly with the presidential election in November.

"In a world where some treat life as something to be debased and discarded, we need your message that all human life is sacred..." the president said.

The pope said freedom "is not only a gift but also a summons to personal responsibility" toward the less fortunate at home and around the world.

"Democracy can only flourish, as your founding fathers realised, when political leaders and those whom they represent are guided by truth and bring the wisdom born of firm moral principle to decisions affecting the life and future of the nation," he said.