WASHINGTON — After days of anti-American violence across the Muslim world, the White House is girding itself for an extended period of turmoil that will test the security of American diplomatic missions and President Obama’s ability to shape the forces of change in the Middle East.


Although the tumult subsided Saturday, senior administration officials said they had concluded that the sometimes violent protests in Muslim countries may presage a period of sustained instability with unpredictable diplomatic and political consequences. While pressing Arab leaders to tamp down the unrest, Mr. Obama and his advisers are left to consider whether to scale back diplomatic activities in the region.


The upheaval over an anti-Islam video has suddenly become Mr. Obama’s most serious foreign policy crisis of the election season, and analysts say it is calling into question central tenets of his Middle East policy. Did he do enough throughout the Arab Spring to help the transition to democracy from autocracy? Has he drawn a hard enough line against Islamic extremists? Did his administration fail to address security concerns? Has his outreach to the Muslim world yielded any lasting benefits?


These questions come at an inopportune time domestically as Mr. Obama enters the fall campaign with a measurable lead in polls. His policies escaped serious scrutiny in the initial days after the attack that killed four Americans in Libya last week, in part because of the furor over a statement by his opponent, Mitt Romney, accusing the president of sympathizing with the attackers. White House officials said they recognized that if not for Mr. Romney’s statement, they would have been the ones on the defensive.


The Egyptian government, responding to administration pressure, cracked down on protesters in Cairo on Saturday.


But images from the past week of American flags being torn down and burned, an Islamic flag being raised and embassies being overrun by angry mobs introduce a volatile element into a re-election effort in which foreign policy has been a strength. Some critics and commentators were already evoking the images of the Iranian hostage crisis that doomed another presidency.


“After Obama’s success in killing Osama bin Laden, in killing Qaddafi and in not blowing up Iraq, I think Obama and his aides figured, ‘We’ve got this box pretty well taken care of,’ ” said Michael Rubin, a Middle East scholar at the American Enterprise Institute and a former Bush administration official, referring to Col. Muammar el-Qaddafi of Libya.


“Now that gets thrown up into the air,” he said. “Instead of Obama being the successful guy that got Bin Laden, we’re talking about Obama as the second coming of Jimmy Carter, and that’s not something the campaign wants to see.”


Mr. Obama came to office vowing to recalibrate America’s relationship with the Muslim world after the Iraq war and gave a high-profile speech in Cairo outlining a new era of fraternity. Caught off guard by cascading revolutions in the Middle East, he eventually supported rebels who overthrew Egypt’s longtime president and ordered airstrikes that helped bring down Colonel Qaddafi, who was later killed.


But he has struggled to find a balance between supporting democracy and guarding national interests in the region as authoritarian governments have been replaced by popular Islamist parties, some unfriendly to the United States. To the extent that the United States supports greater democracy, it may not defuse anti-American rage in a region with no real history of popular rule, and with deep economic troubles. His citing of Libya as a model now looks suspect, and the United States has been powerless to stop a bloody crackdown in Syria.


Administration officials are acutely aware of the risks. They worry that the violence is likely to rage for a while, because with every new protest more people are exposed to the inflammatory American-made anti-Islam video that has fueled so much anger.


“The reality is the Middle East is going to be turbulent for the foreseeable future and beyond that,” said Richard Haass, president of the Council on Foreign Relations and a former State Department official in the Bush administration. “It’s going to present the United States with any number of difficult choices. It’s also going to be frustrating, because in most instances our interests are likely to be greater than our influence.”