The year that Prince Saud al-Faisal was appointed foreign minister of Saudi Arabia, Gerald R. Ford was president of the United States, the Vietnam War ended and Microsoft had just opened its doors.

Prince Saud, a member of the ruling Saud family, is the world’s longest-serving foreign minister. He was appointed in 1975, and for nearly 35 years he has represented a nation whose oil wealth and religious importance to Muslims remains unrivaled. And yet, he said that after all those years, his legacy might be defined more by profound disappointment than by success. His generation of Arab leaders failed, he said, to produce a Palestinian state.

“We have not yet seen moments of joy in all that time,” the prince said in a recent interview in his office here in the Saudi capital. “We have seen only moments of crisis; we have seen only moments of conflict, and how can you have any pleasure in anything that happens when you have people like the Palestinians living as they are?”

This is a time of urgency not only for Prince Saud but also for most of the leaders of Saudi Arabia’s ruling family. After decades in power, age and illness are forcing them to confront their mortality.

King Abdullah is 85 years old, and while still appearing robust, he is old enough to have inspired talk of succession. Crown Prince Sultan, who became defense minister in 1962, returned home on Friday after treatment in the United States for cancer and a period of convalescence in Morocco. The expectation now is that the next king will be Prince Nayef, 76, the interior minister since 1975, who has close ties to the nation’s conservative religious community.

Prince Saud is 69 and was once seen as a potential candidate for monarch. But he, too, has serious health issues. He recently returned home after having surgery in California. While the details of his health problems remain private, his physical appearance has clearly diminished. A once vigorous man who commanded his gold-trimmed Arabian robes with flair, he now holds his gown wrapped tight like a blanket. He struggles to hold himself upright, while his head and neck tip forward.

His staff says that he is back to his relentless schedule, traveling the world, holding meetings, consulting with the king. In the interview he was precise, carefully choosing his words. His message was that the central factor in regional stability remained the Israeli-Palestinian conflict.

During his career, he has been the public face and voice of a nation that has preferred to remain in the background, pursing quiet diplomacy, using its oil wealth to spread its influence and agenda. But that approach, the Saudis’ ties with Washington and a willingness to push for peace with Israel have also earned the nation enmity from around the region.

“When he comes to assess his 35 years as foreign minister, from the first day until today, what has he accomplished for the Palestinian cause? Nothing,” said Emad Gad, an international affairs expert at the Ahram Center for Political and Strategic Studies in Cairo. “And he is the foreign minister of the No. 1 or No. 2 country in the region for more than 30 years.”

That assessment clearly stings for a man who has been well regarded for his poise and intellect in capitals around the world, but it is one he does not deny.

“Peace until now has been like holding water or sand in your hand,” the prince said. “You see the amount of water, you think you can hold something in your hand, but it falls away. Sand is the same thing. So unless there is something to hold in your hand and to point to as a success and as an achievement, then you have done nothing.”

His full name is Prince Saud bin Faisal bin Abdul Aziz al-Saud. His father, King Faisal, who forged the close ties between Riyadh and Washington, was assassinated in 1975 when a nephew shot him at point-blank range. One brother, Prince Turki, was the head of Saudi intelligence who went on to serve as ambassador to Britain and for a short time as ambassador to the United States. Another brother, Prince Khalid, is the governor of Mecca.

Prince Saud has a degree in economics from Princeton, and his official profile says that he speaks seven languages. He is married, with six children, and is a warm man, with a sense of humor and a willingness uncommon within the royal family to speak publicly and to talk to reporters. As the representative of an absolute monarchy, he has influence, but not final say.

“The influence of individuals is limited because it is the vision of the king that prevails through his advisers,” Mr. Gad said. “Prince Saud served for three kings, with each having his own leanings. He is not a decision maker; he executes policies.”

These days, he is promoting the king’s initiative, which calls for Arab unity, a project that so far has gained attention but little traction. He also offered his thoughts on some of the hot topics of the day. He said that Lebanon could never be truly sovereign as long as the Shiite militia Hezbollah “owns more arms than the military force of the country.”

He said that Iran should never be allowed to have nuclear weapons, and that he was “suspicious” of Iranian claims to be pursuing a peaceful nuclear program. He said Israel also should be pressed to give up its nuclear arsenal.

“The danger of this is that there has never ever been a weapon that has been brought in this region but that has not been used,” he said.

But as he pulled his robe close and reflected on his tenure as Saudi Arabia’s chief diplomat, his thoughts returned to the Palestinians. The burning crisis, he said, has ruined Palestinian lives and left the region staggering from crisis to crisis.

“The absolute backing of the United States to Israel has had the effect that rather than making Israel safe for making peace, it has made Israel see the option of living in the area without the acceptance of the people of the area,” he said, “and this has led to many years of conflict between Israel and the Palestinians.”