The Saudi government must also manage the rising popular demand for greater action to defend the rebels against the Syrian government, widely seen here as a proxy for Saudi Arabia’s arch-nemesis, Iran. Behind these political fault lines lies a deep sectarian hostility: Saudis are increasingly angry about the mistreatment of their fellow Sunni Muslims in Syria by an Alawite regime they see as heretical.

“There is deep anger,” said Abdelaziz al-Gasim, a prominent lawyer in Riyadh with a reformist reputation. “People want the government to do more.” The calls for greater involvement are a rare point of accord between Saudi liberals and conservatives, he added, though they are more visible on the free zone of Twitter than in traditional media.

Already, regional Islamist funding networks are being built up, Mr. Gasim said. “These are private channels with people in Kuwait and Qatar, and you cannot control them — there are deep business relationships in the gulf,” he said. “And the majority of them are within the Islamic movement, because the more nationalist or secular movements in Syria have no relationship with Saudi society.”

To some extent, the Saudi and Qatari governments have themselves to blame, because the major pan-Arab satellite TV stations they control — Al Arabia and Al Jazeera, respectively — have done more than any other outlets to stoke anger against Syria’s government and urge sympathy with the rebels. Both stations have been accused of being little more than rebel mouthpieces, and they have played on sectarian fears and hatreds. In one recent and much-repeated teaser on Al Arabia for a news segment about Syria, a man with an anguished face clutches a wounded child and shouts into the camera: “Our children are dying because of Iranian fatwas!”

The Saudi government has not officially acknowledged providing arms to the rebels, and the public face of its aid has been charitable support, including a much publicized donation campaign for Syrian refugees during the holy month of Ramadan in July and August. The government is also paying the salaries of many defected Syrian officers, and financing medical assistance to Syrian refugees.

But at the Turkish border town of Antakya late last month, Syrian rebels spoke openly of the Saudi and Qatari intermediaries who dole out weapons on behalf of their governments. The chief Saudi supplier is said to be a Lebanese figure named Okab Saqr, who belongs to the political coalition of Saudi Arabia’s chief ally in Lebanon, Saad Hariri.

“The amounts are not that much,” said Maysara, 40, a lean rebel commander from the northern town of Saraqib, who withheld his last name for safety reasons. “They deliver weapons once every few weeks.” In one recent shipment, he said, a 200-man fighting brigade received six Russian-made AS Val assault rifles, and thousands of rounds of ammunition.