WASHINGTON » As the Obama administration grapples with a cascade of uprisings in the Middle East, it has come to a stark recognition: The region’s monarchs are likely to survive; its presidents are more likely to fall.

In the rapidly changing map that stretches from Morocco to Iran, two presidents have already tumbled: Hosni Mubarak of Egypt and Zine El Abidine Ben Ali of Tunisia. Administration officials said they believe that Yemen’s authoritarian president, Ali Abdullah Saleh, is in an increasingly tenuous position.

Yet in Bahrain, King Hamad bin Isa Al Khalifa has so far managed to weather a surge of unrest, winning U.S. support, even though his security forces were brutal in their crackdown of protesters. Officials believe that King Abdullah of Saudi Arabia is also unlikely to be dethroned, while the emirs of the Persian Gulf have so far escaped unrest. Even in Jordan, where serious protests erupted, King Abdullah II has maneuvered to stay in power, although he still has to contend with a restive Palestinian population.

This pattern of kings holding on to power is influencing the administration’s response to the crisis: The United States has sent out senior diplomats in recent days to offer the monarchs reassurance and advice — even those who lead the most stifling governments. But it is keeping its distance from autocratic presidents as they fight to hold power.

By all accounts, that is more a calculation of U.S. interests than anything else.

"What the monarchies have going for them are royal families that allow them to stand above the fray, to a certain extent," said Kenneth M. Pollack, the director of the Saban Center for Middle East Policy at the Brookings Institution. "It allows them to sack the government without sacking themselves."

Many of the monarchs have run governments every bit as repressive as the presidents’. And the U.S. calculation of who is likely to hang on to power has as much to do with the religious, demographic and economic makeups of the countries as with the nature of the governments.

Arab presidents pretend to be democratically chosen, even though most of their elections are rigged. Their veneer of legitimacy vanishes when pent-up grievances in their societies explode. Most of the presidents oversee more populous countries, without the oil wealth of the gulf monarchies, which would enable them to placate their populations with tax cuts and pay raises, like the kings of Saudi Arabia and Jordan have done recently.

The Americans acknowledge that they have no choice but to support countries like Saudi Arabia, and that all of the situations could change rapidly.

A case in point is Libya, where Moammar Gadhafi — neither a king nor a president — has been brought to the verge of collapse with dizzying speed.

On Thursday, the administration failed again to evacuate diplomats and other U.S. citizens from Libya. A ferry chartered by the U.S. government remained tied up at a pier in the capital, Tripoli, unable to sail to Malta because of heavy seas in the Mediterranean.

The 285 passengers are safe, according to State Department spokesman Philip J. Crowley, but they cannot leave the ship, which he said is guarded by Libyan security forces. A hotel across the street from the pier has been the site of gun battles between rebels and loyalists of Gadhafi, witnesses said.

The stalled evacuation has led the Obama administration to temper its condemnations of Gadhafi’s government, because officials worry that the Libyan government could take Americans hostage. But Crowley said Thursday that the United States would support a European proposal to expel Libya from the U.N. Human Rights Council, when it meets in Geneva on Monday.

Unlike in the case of Egypt, where President Barack Obama spoke by phone with Mubarak several times during the crisis there, neither he nor any other U.S. official has spoken with Gadhafi since the violence erupted. Secretary of State Hillary Rodham Clinton was unable to reach the foreign minister, Moussa Koussa, Crowley said, citing a technical glitch. The undersecretary of state for political affairs, William J. Burns, did speak twice with Koussa, he said, and conveyed the administration’s "concern" that Libya continue to cooperate with the evacuation.

The spotty U.S. communication with Libya contrasts with the regular phone calls Obama and Clinton have held with Arab monarchs. Abdullah of Saudi Arabia pressed Obama in at least two conversations to back Mubarak. Since his ouster, an administration official said, Saudi officials have expressed some misgivings about their support for the former Egyptian leader.

So far, the kings appear to be hanging on.

The administration is sanguine that the Saudi royal family will survive any upheaval, although some acknowledge that they misread the prospects for change in Egypt. Earlier this week, Abdullah, returning home from three months of medical treatment abroad, announced a $10 billion increase in welfare spending to help young people marry, buy homes and open businesses.

The administration has urged Saudi Arabia not to impede Hamad’s attempt to undertake reforms in Bahrain, an island connected to Saudi Arabia by a causeway and dependent on the Saudis for political and economic support. Saudi Arabia is rattled by the prospect of Bahrain’s Shiite Muslim majority’s gaining more political power, at the expense of its Sunni rulers, in part because Saudi Arabia has a substantial Shiite population in its east.

U.S. officials have sought to keep the focus on what they insist have been concessions made by Bahrain, where the Navy’s Fifth Fleet is stationed, as a sign that the protests can prod the king, and the crown prince who will head the dialogue with the protesters, in the right direction.

Similarly, in Jordan, Abdullah, who faces a tricky situation because of his majority Palestinian population, has signaled a willingness to cede some power to an elected government or parliament. U.S. officials and independent experts say that they think that could allow him to hang on to power. The administration’s clear hope is that all these kingdoms will eventually be constitutional monarchies.

"That approach to Jordan or Bahrain is the right approach; these are countries that have moved in the right direction, but not enough," said Elliott Abrams, a Middle East adviser in the Bush administration who has been a frequent critic of the Obama administration. "Constitutional monarchy is a form of democracy."

There has been far less unrest in other Persian Gulf states, like the United Arab Emirates, Qatar or Kuwait — in part, experts say, because they are essentially regal welfare states, where citizens pay no taxes and are looked after by the government. In the United Arab Emirates, for example, when one citizen marries another citizen, the government helps to pay for the wedding and even to buy a home.

Even so, an administration official noted, the crown prince of Abu Dhabi, Mohammed bin Zayed, recently toured less prosperous parts of the United Arab Emirates to hold town-hall-style meetings — at least a nod to democratic rule.

"The truly wealthy societies like Qatar, the UAE and Kuwait have greater advantages," said Ted Kattouf, a former U.S. ambassador to Syria. In many ways, he added, "the monarchies have more legitimacy than the republics."

In Yemen, a lack of legitimacy is plaguing Saleh and the prospect of instability there poses national security problems for the United States, which has had the government’s support for counterterrorism operations. Protesters are demanding his resignation even after he pledged not to seek re-election. The administration is pushing Saleh — who has played off factions in his country to cling to power for 30 years — to revive a stalled effort at constitutional reform, although an official expressed pessimism about the likelihood of progress.

"The republics — and hence, the presidents — are the most vulnerable because they’re supposed to be democracies but ultimately are not," said an Arab diplomat, who spoke on condition of anonymity. "They pretend people have a voice, but this voice doesn’t exist. With the monarchy, no one’s pretending there’s a democracy."