Crown Prince Fahd becomes King of Saudi Arabia at one of the most critical moments in his country's postwar history.
From outside the kingdom is challenged on two fronts: most immediately from across the Gulf in Iran by Ayatollah Khomeini's rampant Shia Muslim fundamentalism, flushed in recent weeks by the defeat it has inflicted on Iraq; and, on its other flank, by Israel's savaging of the Palestinians in Lebanon.
But as on the last two transfers of the Saudi crown, the solidarity of the Saudi royal family has asserted itself in a moment of danger.
In Saudi Arabia, royal succession does not depend exclusively on primogeniture but is the result of prior consensus among the senior princes. Thus King Khalid's passing June 13 has been promptly followed by the transfer of the crown to his designated successor, Crown Prince Fahd, his half-brother.
The new crown prince is another half-brother of the new king and two years his junior, Prince Abdullah, head of the National Guard. Until now, he has been second deputy prime minister. His promotion in the succession had already been agreed in advance.
The late King Khalid, though much respected for his good relations with the traditional forces within Saudi Arabia, was to a degree a figurehead monarch. Day-to-day running of the country since 1975 (when he succeeded the assassinated King Faisal) has been in the hands of Prince Fahd - particularly in foreign affairs.
Though decisions have usually been by family consensus, Fahd has perhaps been the single most important figure in shaping policy. But Fahd has not acquired for himself among the traditionalists at home the same reputation for piety and conservative seemliness as had King Khalid.
Of the new King, Wiiliam B. Quandt of the Brookings Institute has written:
''In some circles, (Fahd) has been referred to as pro-American, which is a great oversimplification and can be very misleading. Nonetheless, Fahd appears to value the relationship with the US and seems to believe that Washington can be persuaded to support Saudi Arabia without threats and confrontation. In his dealings with Washington, Fahd is often indirect, elusive and soft-spoken. He never directly brandishes the oil weapon and seems aware of the risks of doing so.
''In inter-Arab politics, Fahd is a centrist, seeking consensus and trying to avoid Saudi Arabia's isolation. He is less anti-Egyptian than many Saudis . . .
''If Fahd becomes king, he may try to be more assertive in setting the broad lines of Saudi policy. This could produce some resistance from other members of the family, but the patterns of the past provide little reason to expect serious splits unless Fahd tries to govern without regard for the views of others in the family. Periods of stress seem to bring the princes closer together rather than to exacerbate their differences . . . Consensus is not just a traditional virtue. It is also the key to the Saudi family's survival.''
Of the new crown prince, Abdullah, Mr. Quandt writes:
''On occasion Abdullah is mentioned as heading an anti-American faction of the royal family. While he may be less committed to the US-Saudi 'special relationship' than Fahd, there is little evidence to support the view that Abdullah is much different from other members of the royal family in his basic foreign policy views. Indeed, there is considerable reason to believe that he is enough of a political realist to want to develop his own channels to communicate with Washington.''
Outsiders are often fascinated by the possible influence among the many sons of the late King Abdul Aziz (founder of the modern Saudi dynasty who ruled from 1902 to 1953) of the seven Sudeiry brothers. These have a common mother in Hussah bint Al-Sudeiry. The new King Fahd is one of them.
Crown Prince Abdullah is not one of the seven, so there is something of a balance still at the top. But there is a Sudeiry brother, Prince Sultan, Minister of Defense, who is widely thought to want one day to be king. It will be interesting to see if the senior princes now confirm him in the line of succession left vacant by Prince Abdullah's advancement as heir to the new king.