High anxiety reigns in Saudi Arabia. The neighborhood is in upheaval, the hated Shiites are ascending, and there is turbulence in the higher circles of the ruling family.

The Saudi ambassador to Washington — the very senior Prince Turki Al-Faisal, who served for 25 years as chief of intelligence — abruptly resigned last week and took off for home.

Just before his departure, the prince engineered leaks to the American press warning that Saudi Arabia would step in with weapons and fighters to back the Iraqi Sunnis if they appeared to be losing the sectarian war in Iraq.

Indeed, many Saudis in the Wahhabi Najd region are agitated. Two weeks ago, 30 senior religious figures in the kingdom issued fiery statements lamenting the killing of Sunnis in Iraq by the “heretics” — their description of the Shiites next door. The move was reminiscent of the call to jihad in the 1980s against the Soviet Union in Afghanistan, which thousands of Saudis embraced, flocking to the holy war there.

Just two days after Thanksgiving, King Abdullah abruptly summoned Vice President Cheney to Riyadh. The king told his old friend that America couldn’t have any dialogue with Iran, that it shouldn’t think about leaving Iraq until the country is stable, and that Iran and Syria couldn’t be allowed to spread their hegemony to Iraq and Lebanon.

Is the Saudis’ growing paranoia justified?

A rising Shiite crescent is indeed spreading to Shiite-controlled Iraq from Iran; to Lebanon through Iran’s armed militia, the Shiite proxy Hezbollah; and as far as the Gaza Strip, where Hamas is now receiving millions of dollars from Iran, as well as weapons and military training from Hezbollah.

The upset of Sunni domination in the greater Middle East began with the Iranian revolution of 1979, which introduced a sober Shiite challenge to Sunni supremacy in Islamic jurisprudence and created militias and adherents even among some Sunnis in the region. Now the Saudis fear turbulence in the kingdom of Bahrain, which is linked to Saudi Arabia by bridge and has a population of 700,000, 60% of them Shiites unhappy with their Sunni rulers and partial to Shiite Iran.

Inside Saudi Arabia, the demographic sands are shifting. In essence, the kingdom contains three regions — Najd, Hejaz, and the oil-producing Eastern province.

The weightiest, the epicenter of the Wahhabi-dominated culture and the country’s heartland, is the core region of Najd, which is teeming with influential figures inveighing against a Shiite Iraq.

In this region, which includes the 5 million citizens of the Saudi capital, Riyadh, Iraq is a hot topic because of the blood ties uniting the huge Shammar tribe that spreads over both Najd and the Sunni regions of Iraq. Altogether, Shammar clans number as many as 15 million Bedouin Arabs spread over Iraq, Syria, and the Gulf region, with many in Saudi Arabia, creating family bonds that supersede national borders.

Saudi affairs experts note that King Abdullah’s mother, for example, was a member of the Shammar tribe. His wife is a Shammar Iraqi.

Arab intelligence officials have pointed out that among those killed by American forces and Shiite death squads over the past two years were many Iraqis with relatives in Saudi Arabia. Honor and revenge, therefore, beckon.

Amid all this, new rivalries have sprung up among the Saudi princes as the royal clans question the king’s abilities to handle a situation that is becoming critical.

The religious fanatic wing of the family, backed by the Wahhabi preachers, is calling for a new jihad in Iraq.

The Faisal brothers — the foreign minister, Saud, and the Washington ambassador, Turki — want to shore up their home base, which represents the pro-Western, liberal wing of the family. The former Saudi ambassador to America, Prince Bandar bin Sultan, is mounting his own campaign to dominate King Abdullah’s foreign policy and undermine the Faisal clan.

All this suggests that 2007 will be an eventful year for Iraq, the region, and especially Saudi Arabia.