Nayef, who died Saturday at 78, was seen as a hard-line conservative whose accession to the throne might have tilted rightward the delicate balance that King Abdullah has struck between traditionalist Muslim clerics and a younger generation that wants more freedom for women, greater openness and a freer political culture.

The crown prince slot is now likely to go to Prince Salman, who was named defense minister last year and is seen as a more organized, less rigid and potentially more change-oriented leader than some other senior princes. Salman visited Washington this year for friendly talks at the White House and Pentagon.

Nayef served as Saudi interior minister for an astounding 37 years. He maintained order in the kingdom in an alliance with the Saudi religious establishment. That pact grew problematic, to put it mildly, after Saudi religious fanatics in Al-Qaeda helped organize the Sept. 11, 2001 attacks — a link Nayef at first dismissed. But he grew more adept at cooperating with the CIA and other Western intelligence services, once he realized that the kingdom itself was at risk.

U.S. officials grew to have high regard for Nayef’s sons, Mohammed bin Nayef, the chief of counterterrorism, and Saud bin Nayef, who acted as his father’s chief of staff. The hope was that they could soften their father’s conservative leanings, but U.S. officials doubted that Nayef could ever be a popular king in the way that Abdullah has become.

King Abdullah, at 88, remains a potent figure in the Arab world, and Saudis say that as he ages, he increasingly lets personal grudges drive policy. He’s still angry, for example, that the U.S. connived in toppling Hosni Mubarak as president of Egypt last year, and Saudi pressure is one big reason the Egyptian military has been waging what amounts to a counter-revolution in recent days, dissolving parliament and extending military rule. Abdullah is said to loathe Syrian President Bashar al-Assad and Iraqi Prime Minister Nouri al-Maliki, regarding both as tools of Iran, and to mistrust Turkish Prime Minister Recep Tayyip Erdogan, whose country is a traditional Saudi rival.

U.S. officials had said, prior to Nayef’s death, that it would be much better for Saudi stability if Abdullah outlived him and remained on the throne for a while longer. Abdullah’s personal popularity within the kingdom remains high, especially among Saudi women, who regard him as something of a protector.

Saudi life after Abdullah is still a mystery but a slightly less threatening one if, as expected, Salman takes the crown prince position. As evidence of Salman’s consensus-oriented approach to politics, one Saudi notes that over his many decades as governor of Riyadh, he was often the senior prince who was asked to resolve delicate disputes within the family.