But as many as a dozen additional operations have been canceled in the past four years, often to the dismay of military commanders, senior military officials said. They said senior administration officials had decided in these cases that the missions were too risky, were too diplomatically explosive or relied on insufficient evidence.

More than a half-dozen officials, including current and former military and intelligence officials as well as senior Bush administration policy makers, described details of the 2004 military order on the condition of anonymity because of its politically delicate nature. Spokesmen for the White House, the Defense Department and the military declined to comment.

Apart from the 2006 raid into Pakistan, the American officials refused to describe in detail what they said had been nearly a dozen previously undisclosed attacks, except to say they had been carried out in Syria, Pakistan and other countries. They made clear that there had been no raids into Iran using that authority, but they suggested that American forces had carried out reconnaissance missions in Iran using other classified directives.

According to a senior administration official, the new authority was spelled out in a classified document called “Al Qaeda Network Exord,” or execute order, that streamlined the approval process for the military to act outside officially declared war zones. Where in the past the Pentagon needed to get approval for missions on a case-by-case basis, which could take days when there were only hours to act, the new order specified a way for Pentagon planners to get the green light for a mission far more quickly, the official said.

It also allowed senior officials to think through how the United States would respond if a mission went badly. “If that helicopter goes down in Syria en route to a target,” a former senior military official said, “the American response would not have to be worked out on the fly.”