In part because of concerns about diversion of funds, only a sliver of the money from the American aid program actually goes to the Egyptian military. Instead, the Pentagon directly pays American companies that it has chosen to manufacture and ship the tanks, planes, guns and ammunition to Egypt.

Egyptian opposition groups have said that Mr. Mubarak and senior generals were nonetheless able to divert money. But American officials insist that the design of the program  known as Foreign Military Sales  ensures that money cannot be stolen.

Edward W. Ross, a former official at the Defense Security Cooperation Agency, which oversees the sales, said he was irked by allegations that Egyptians could have pocketed money. “That money goes to the Federal Reserve,” he said, “and then it is only released to a U.S. contractor.”

Keeping Aid Flowing

Even so, the United States has considerably less control over how goods are used once they arrive in Egypt. In interviews, several former American military officials said that keeping the aid flowing often seemed to trump questions of how effective it was. Some of them asked to remain anonymous because they did not want to alienate the Egyptian military. The yearly $1.3 billion, one retired colonel explained, is viewed as “an entitlement.”

At times, American officials have argued with Egyptian generals over whether certain equipment was actually for military use. That was the case with the Gulfstream jets.

The retired colonel, who worked at the American Embassy’s Office of Military Cooperation in Cairo, said that the Egyptians assured him the planes would be used for “mapping,” but that he was skeptical. “It was obvious to us that these were going to be used at least in part for V.I.P. travel,” the colonel said.

Officers tried to block the deal, he recalled, but “our contacts at the Ministry of Defense were applying pressure” to make sure the sale went through.