But while the gains of the Islamic State of Iraq and Syria are impressive, the rebels have their weaknesses. For the most part, they are lightly armed fighters whose logistical lines stretch back to northeast Syria and who often travel in vulnerable vehicles. Some of the group’s fighters have made their way to Falluja and Iraq’s Anbar Province through the Euphrates River Valley, while others have moved through northern Iraq to Mosul.

A major question for the Obama administration would be whether to also strike targets in Syria as the group is moving freely across the Syria-Iraq border.

“We can do a lot of damage to ISIS in Iraq and Syria pretty quickly,” said Jack Keane, the retired Army general who served as vice chief of staff of the Army, and who said that airstrikes could also help restore the confidence of Iraqi troops.

Military experts cautioned, however, that air power is not a panacea. They said that the United States needs to provide better intelligence to the Iraqis and must persuade Mr. Maliki to replace incompetent but politically connected commanders. The United States, they said, should also send American military planners to help devise and coordinate military operations.

American Defense officials in the meantime warned that the Maliki government must include prominent Sunnis and Kurds in the government and take steps to bridge the sectarian divisions that have brought the country to the edge of civil war.

A frustrated-sounding Pentagon press secretary, Rear Adm. John Kirby, said at a briefing on Friday that the United States is “disappointed with the performance of some of these units,” which failed to hold Mosul and a number of other cities from the advances of the Al Qaeda-inspired Islamic State of Iraq and Syria group.

During the years that American forces were based in Iraq, they often supplied air power for Iraqi units that confronted Sunnis extremists or Shiite militants. When Mr. Maliki ordered his forces to retake Basra from Shiite militants in 2008, Iraqi forces suffered serious setbacks until Gen. David H. Petraeus, who was then the American commander, sent American warplanes, AC-130 gunships, Predator drones and American advisers to help the Iraqi military.