President Obama’s visit with Saudi Arabia’s King Abdullah in March was intended to reassure Saudis of the U.S. commitment to the relationship. (© Kevin Lamarque / Reuters/REUTERS)

The worst rupture in 40 years in U.S.-Saudi relations has been eased — but not healed — by a series of measures aimed at restoring damaged trust.

In a sign of the significance of the relationship, both governments have made strenuous efforts to repair the rift, which emerged after President Obama stepped back last summer from his “red line” on any use of chemical weapons by Syria and declined to launch airstrikes against its government.

But differences over Iran, Egypt and, above all, Syria — which has become something of a personal mission for Saudi King Abdullah — linger, leaving the alliance that has underpinned the balance of power in the Middle East for decades still fraught.

The reversal on Syria came as a bitter blow to Riyadh, not only because an opportunity to topple President Bashar al-Assad was lost but also because of the broader message it sent about the reliability of the United States, upon whose security guarantees the oil-rich kingdom has relied for six decades.

“Obama has no political will at all, not only in Syria but everywhere,” said Abdullah al-Askar, head of the foreign affairs committee in the kingdom’s advisory Shura Council, reflecting the widespread perception that the United States has lost interest in the Middle East. “The disappointment with him is felt all over the Arab world.”

Obama’s visit with Abdullah in March, intended to reassure Saudis of the U.S. commitment to the relationship, has been followed by a flurry of U.S. delegations from various branches of government. Among the visitors was Defense Secretary Chuck Hagel, who this month asserted the United States’ determination to remain engaged in a region that produces most of the world’s oil.

Saudi Arabia, meanwhile, has taken steps to retool its own approach to the Syrian conflict to address some of the concerns underpinning U.S. reluctance for greater involvement, including measures to curtail the proliferating influence of jihadists over the rebels.

A tough new anti-terrorism law outlawed the main al-Qaeda-linked Syrian groups and introduced penalties for Saudis who volunteer to fight in Syria. About 1,500 of them have traveled there, according to the government.

The king has also replaced the man most identified with the rupture, Prince Bandar bin Sultan, whose outspoken criticisms of the U.S. failure to bomb Syria brought to light the depth of Saudi anger with its closest ally.

Saudi officials insist that Bandar stepped down only for health reasons. But Western diplomats said Bandar, who served for many years as the Saudi ambassador in Washington and was renowned for his ability to influence U.S. decision-making, may also have been ousted because he failed to deliver an American response on Syria.

The new emphasis on counterterrorism reflects genuine Saudi concerns about the rapidly growing influence of extremists on the Syrian opposition, which only seems to have deterred Western interest in helping the rebels without doing anything to accelerate Assad’s fall, Saudi officials say.

Fears of the kind of blowback the kingdom faced after Saudi volunteers returned from fighting the Soviet Union in Afghanistan in the 1980s were intensified after authorities uncovered a purported plot last month by 106 people to carry out attacks in Saudi Arabia. Of the suspects, 62 were detained and 44 are still being sought.

At least some of them had had Skype conversations with members of the al-Qaeda-inspired Islamic State of Iraq and Syria, in which the assassination of Saudi officials was discussed, said Gen. Mansour al-Turki, a spokesman for the Interior Ministry.

“Saudi Arabia’s interests will not be served by al-Qaeda,” he said. “We do not want al-Qaeda to be involved in Syria, or to see our people involved there.”

But the kingdom has not abandoned its core goal of ousting Assad or its hope that the United States will eventually step up to help propel his departure, said Prince Turki al-Faisal, a former director of Saudi intelligence who heads the King Faisal Center, a Riyadh think tank.

The Obama administration has in recent weeks shown a greater willingness to allow weapons to flow to Syrian rebels. U.S.-made TOW antitank missiles appeared in rebel hands last month for the first time after the United States authorized their delivery.

Ramped-up measures to help the Syrian opposition also are expected to be announced by Obama in a speech Wednesday, including for the first time direct Pentagon involvement in arming and training the rebels.

But it seems unlikely that the measures will go far enough to satisfy Saudi hopes for a game-changing gesture that would force Assad to negotiate his demise, such as the supply of antiaircraft missiles, which Saudi officials have been pushing the Obama administration to provide.

“The disappointment will obviously increase if there is not more support for the opposition,” Faisal said. “Whatever policy the world has established for Syria to prevent the killing of Syrians is not working.”

“You can’t have negotiations without leveling the playing field, and why would Assad negotiate if he is gaining ground?” Faisal added, pointing to more than a year of setbacks for the rebels on the battleground.