The C.I.A. has not commented on Mr. Petraeus’s trip, made to a region he knows well from his days as the Army general in charge of Central Command, which is responsible for all American military operations in the Middle East. Officials of countries in the region say that Mr. Petraeus has been deeply involved in trying to steer the supply effort, though American officials dispute that assertion.

One Middle Eastern diplomat who has dealt extensively with the C.I.A. on the issue said that Mr. Petraeus’s goal was to oversee the process of “vetting, and then shaping, an opposition that the U.S. thinks it can work with.” According to American and Arab officials, the C.I.A. has sent officers to Turkey to help direct the aid, but the agency has been hampered by a lack of good intelligence about many rebel figures and factions.

Another Middle Eastern diplomat whose government has supported the Syrian rebels said his country’s political leadership was discouraged by the lack of organization and the ineffectiveness of the disjointed Syrian opposition movement, and had raised its concerns with American officials. The diplomat, who spoke on the condition of anonymity because he was discussing delicate intelligence issues, said the various rebel groups had failed to assemble a clear military plan, lacked a coherent blueprint for governing Syria afterward if the Assad government fell, and quarreled too often among themselves, undercutting their military and political effectiveness.

“We haven’t seen anyone step up to take a leadership role for what happens after Assad,” the diplomat said. “There’s not much of anything that’s encouraging. We should have lowered our expectations.”

The disorganization is strengthening the hand of Islamic extremist groups in Syria, some with ties or affiliations with Al Qaeda, he said: “The longer this goes on, the more likely those groups will gain strength.”

American officials worry that, should Mr. Assad be ousted, Syria could erupt afterward into a new conflict over control of the country, in which the more hard-line Islamic groups would be the best armed. That depends on what happens in the arms bazaar that has been feeding the rebel groups. In several towns along the Turkey-Syria border, rebel commanders can be found seeking weapons and meeting with shadowy intermediaries, in a chaotic atmosphere where the true identities and affiliations of any party can be extremely difficult to ascertain.

Late last month in the Turkish border town of Antakya, at least two men who had recently been in Syria said they had seen Islamist rebels buying weapons in large quantities and then burying them in caches, to be used after the collapse of the Assad government. But it was impossible to verify these accounts, and other rebels derided the reports as wildly implausible.