The course Obama intends to take if confronted with proof of a chemical attack is equally unclear. The Pentagon has prepared calibrated options, ranging from airstrikes to sending troops to seize weapons sites. But officials said they haven’t taken the advance steps necessary to carry out such orders because planning has been hobbled by concerns about the political backlash to a potential U.S. intervention as well as struggles to coordinate with regional allies.

“If we had to go in tomorrow, I’d say we aren’t ready,” said an Obama administration official involved in preparations for securing Syria’s chemical weapons. “One thing we want to avoid is having one group securing the sites and another group bombing them.”…

U.S. officials said there is likely to be scant physical evidence by the time experts reach the village where last week’s attack occurred. As a result, experts must rely mainly on reports from witnesses and monitoring the symptoms of those who may have been exposed.

The CIA, the National Security Agency and other spy services have expanded their collection efforts against Syria over the past year. But U.S. officials said that the CIA has not established a presence in the country and that the scope of the conflict has precluded it from distributing sensors that could detect chemical attacks.

Asked whether such devices were being used, one senior U.S. official said, “I wish.”