RIYADH, Saudi Arabia, Aug. 1 - King Fahd bin Abdel Aziz al-Saud, Saudi Arabia's long-ailing monarch who oversaw one of the country's greatest periods of growth while underwriting the spread of fiercely conservative Islam abroad, died Monday morning in the Saudi capital, ending a 23-year reign.

The death of King Fahd, 82, marked the end of a decade-long transition of power that began when he suffered a debilitating stroke in 1995 and put his half-brother, Crown Prince Abdullah bin Abdel Aziz, in control of the country. Shortly after the king was pronounced dead on Monday, Prince Abdullah, 81, became Saudi Arabia's sixth monarch. [Obituary]

During King Fahd's reign he and the royal family found a marriage of convenience with Wahhabism, the conservative branch of Islam that in its more radical forms helped fuel the rise of militancy in far-flung reaches of the Muslim world. But after the emergence of Osama bin Laden in the 1980's and Al Qaeda in the 1990's; the Sept. 11 attacks in 2001, in which 15 of the 19 hijackers were Saudis; and after a later bombing campaign in the kingdom itself, the Saudi rulers grudgingly admitted that their seeming tolerance of the extremism was beginning to threaten their own grip on power.

In an emotional announcement, the Saudi information minister, Iyad bin Amin Madani, confirmed the king's death on state television on Monday morning. "With all sorrow and sadness, the royal court in the name of his highness Crown Prince Abdullah bin Abdel Aziz and all members of the family announces the death of the Custodian of the Two Holy Mosques, King Fahd bin Abdel Aziz," Mr. Madani said, pausing several times to fight back tears as he read from a statement.

King Fahd died after a two-month battle with pneumonia. Immediately after he was pronounced dead, members of the royal family are said to have had a secret meeting to select the new king and heir.

The transition of power in one of America's most strategically important allies on Monday occurred with few surprises. With Prince Abdullah acting as the de facto regent already, the most critical succession was complete in all but name, analysts said. The rise of Prince Sultan bin Abdel Aziz al-Saud, the long-serving minister of defense and aviation, as crown prince, meanwhile, also proceeded as planned, leaving little in the way of uncertainty.

There was a message of continuity to be delivered in that efficiency - an assurance that there would not be any major changes in international or domestic policies. Saudi officials said they expected that, if anything, relations with the United States might grow closer, because the new king has a warm relationship with President Bush.

For Abdullah, who has fashioned himself as a reformer in a land where conforming to tradition is a virtue, the challenge now is to make good on longstanding promises for change. In his nine years as the de facto ruler of the country, he pushed for changes that included the nation's first popular elections, which were held this year to elect local councils.

He also moved the education of girls from the control of the religious authorities to the Ministry of Education. And he has worked to balance close relations with the United States, which is perceived by many in the royal family as essential for national and regional security, against rising anti-Americanism among many of his nation's citizens.

But it remains to be seen whether King Abdullah has the fundamental power to challenge Saudi Arabia's imbedded powers, including the infamous vice police, the religious clergy and more than a thousand royals all vying for position and a hand at the country's purse strings. He may push for greater citizen participation in government, more rights for women and amnesty for some political prisoners, political analysts said.

"We're pinning an awful lot on this one personality," said Toby Jones, the Persian Gulf analyst for the International Crisis Group, who sees the king and his crown prince as the collective flag-bearers for change. "But they're basically not democratic reformers. They're interested in adjusting the political system but not interested in fundamentally changing it."

Stability is a bedrock principle in the Middle East, and in particular in Saudi Arabia, whose dynasty was forged in the 18th century through an alliance between a tribal leader, Muhammad bin Saud, and a religious leader, Muhammad bin Abdul Wahhab, who preached a puritanical form of Islam that sought to restore Islam from what they saw as heresies, superstition and deviance.

Even as the royal family pulled together quickly to head off any vacuum in power, the new king is already well along in years, and his crown prince was born in 1928. The royal family is thousands strong, including older brothers and relatives, who feel that by tradition it is their right to ascend to power, as well as many younger princes who want to see the next generation have a chance at leading.

For those reasons, many analysts looked to the still vacant third spot in the royal chain of command for any possible fault lines and windows of change in the family - and for a possible indication of the nation's future leadership. The unofficial third-in-line is often granted the title of second deputy prime minister, a role Prince Sultan held.

The expectation is that post will go to Prince Nayef bin Abdel Aziz, who is the minister of the interior, but another candidate for the position is Prince Salman, the governor of Riyadh. Some have also talked up the name Prince Bandar bin Sultan, son of the crown prince, who abruptly stepped down as ambassador to the United States last month, though such a candidacy has been dismissed by some close to the royals.

The tension between members of the Saud family, which has sought to use the nation's fabulous oil wealth to catapult it into modernity, and religious leaders, who have tried to keep out everything from satellite television to nonalcoholic beer, still threatens to tear at the fabric of society.

The divisions, which have created political factions within the royal family, had led to expectations that the succession might be troublesome. The new king often found his efforts at reform challenged by more conservative forces, including the powerful interior minister, Prince Nayef.

But if there were forces in the ruling family that were reluctant to challenge the most radical religious aspects of Saudi society, that changed in 2003 with the bombing attacks on Western housing compounds and soon after on government institutions. That sparked a sea change in the attitude of the government and the society, according to a Western diplomats and experts working in the region.

With the full authority of his position, Abdullah will be able to move with a freer hand. But change, if it comes, will be glacial in pace, and only in accord with other members of the royal family.

"He is an absolute monarch," said Khalid al-Dakhil, a political analyst at King Saud University in Riyadh. "But he must rule by consensus. The royal family is like a political party."

Riyadh was quiet on Monday night as preparations were finalized for a funeral to be held on Tuesday afternoon at the Imam Turki bin Abdullah Mosque, where King Fahd will be buried and noted with just a marker stone. Condolences from around the world poured into Saudi Arabia as news of the king's death spread, and foreign dignitaries were expected to fly in to attend the funeral. An Arab leadership summit meeting scheduled for Wednesday in Egypt was postponed for the occasion.

After the funeral, the new king will participate in a traditional Saudi coronation, called a baya, in which Saudis from all walks of society, including tribal leaders and intellectuals, politicians and ordinary citizens, will visit him and swear their allegiance to him. On Wednesday, the general public will be invited to do the same.

Thousands of Saudis who were on their annual vacations began returning home, with Saudi Arabian Airlines reportedly adding flights to meet the demand.

"I have to go home to the funeral," said one Saudi man who had arrived in Dubai just a day earlier for his vacation only to rush back on Monday. "It is our national duty to see him off."

Hassan M. Fattah reported from Riyadh for this article, and Michael Slackman from Cairo.