From across the Arabian Peninsula, some traveling for two days, hundreds of Muslim clerics, princes, tribal chiefs and dignitaries crowded into a silk-carpeted palace here Wednesday to pledge allegiance to Saudi Arabia's King Abdullah in a traditional Islamic ceremony that sealed his status as the sixth monarch of the world's largest oil exporter.

Known as a bayah, the ceremony is older than the kingdom itself, dating to the days of the prophet Muhammad and the succession of caliphs that followed his death in the 7th century. In ritual and message, it was a reminder of the underpinnings of one of the world's wealthiest nations: a near-absolute monarchy that relies on religion for its legitimacy and is sanctioned by the country's powerful clergy.

The ceremony was the last step in the scripted succession that followed the death of King Fahd bin Abdul Aziz on Monday. It marked Abdullah's formal assumption of the power that he had exercised as crown prince in the decade since Fahd, his half brother, suffered a major stroke.

"At times when shouldering this responsibility, and I feel the weight is too heavy and the trust is great, I will derive help from God, and I ask Him to give me strength to continue the march begun by the founder of the kingdom of Saudi Arabia, the great Abdul Aziz al-Saud, and then his sons," Abdullah, believed to be 82, said afterward in his first televised address as king.

He promised to adhere to the Koran, the Muslim holy book, as the country's constitution and "serve all the people without discrimination."

"I appeal to you to support me and help me carry this trust and don't hesitate to advise me," he said.

The ceremony was a vivid example of how the ancient and modern converge in Saudi Arabia -- especially in its capital, Riyadh, much of it a gleaming, Oz-like city that sprawls across a once-barren desert. At the palace and other royal residences, the diverse peoples of Saudi Arabia gathered: men in uniforms, clerics in turbans, princes in pressed robes and tribal chiefs in checkered head scarves. In a sign of their import, the country's highest-ranking clergy were the first to pledge their allegiance; others waited hours, sometimes in vain.

Their greetings were brief, no more than a few moments. They expressed their loyalty to the king, "except in what would disobey God." Younger relatives of the king kissed his hand or shoulder. Others saluted or shook his hand. With the few words, they upheld one of the oldest Islamic traditions, practiced for centuries by the tribes of Arabia.

"It is a contract between the ruler and the ruled," said Abdel-Rahman Suwayid, a 40-year-old member of the royal family, who waited outside another royal residence where pledges were accepted. "When you give bayah to the ruler," it means "I'm with you, I'm under your order, what you do I obey you. There are no limits to the obedience. When the king decides a matter, you must obey."

At the residence, Sheik Amat Irdan gathered with 300 members of his Salman tribe. Irdan said his father, Sheik Obeid, had pledged allegiance to Fahd 23 years ago. His grandfather, Sheik Birgis, had served in the army of Saudi Arabia's founder. Irdan and the tribesmen had traveled 500 miles by car over a leisurely two days. By nightfall, they waited in chairs on red Persian carpets for their turn.

"It brings us together and aligns us in the same direction," Obeid said, seated next to his brothers on a hot summer night. "We were ready to pay our allegiance to King Abdullah even before they buried King Fahd."

Since Fahd's death on Monday at about age 84, officials have rarely wavered from their theme: Continuity will mark the kingdom's policies. But Abdullah takes power at a time when his country is facing a threat by Islamic extremists and its religious establishment is uneasy with the kingdom's alliance with the United States. For others, expectations are high that the king will move ahead on political and economic reforms that he has until now only tentatively embraced.

"This is the moment when the full weight of responsibility falls on his shoulders," said Prince Saud Faisal, the foreign minister.

King Abdullah, center, is surrounded by Muslim clerics, tribal chiefs and other prominent Saudis before a ceremony in Riyadh to mark his ascension.