Syria's Chemical Weapons Moves Lead U.S. to Be Flexible WASHINGTON - When President Obama first warned Syria's leader, President Bashar al-Assad, that even making moves toward using chemical weapons would cross a "red line" that might force the United States to drop its reluctance to intervene in the country's civil war, Mr. Obama took an expansive view of where he drew that boundary. "We cannot have a situation where chemical or biological weapons are falling into the hands of the wrong people," he said at an Aug. 20 news conference. He added: "A red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized. That would change my calculus. But in the past week, amid intelligence reports that some precursor chemicals have been mixed for possible use as weapons, Mr. Obama's "red line" appears to have shifted. His warning against "moving" weapons has disappeared from his public pronouncements, as well as those of Secretary of State Hillary Rodham Clinton. The new warning is that if Mr. Assad makes use of those weapons, presumably against his own people or his neighbors, he will face unspecified consequences. It is a veiled threat that Defense Secretary Leon E. Panetta repeated Thursday: "The president of the United States has made very clear that there will be consequences, there will be consequences if the Assad regime makes a terrible mistake by using these chemical weapons on their own people." The White House says the president has not changed his position at all - it is all in the definition of the word "moving." Tommy Vietor, the spokesman for the National Security Council, said Thursday that " "moving around" means proliferation," as in allowing extremist groups like Hezbollah, which has training camps near the weapons sites, to obtain the material. Such shifts are nothing new in global standoffs; the Israelis have moved their lines more than a half-dozen times in recent years when talking about how close they would allow Iran to get toward the capacity to build a nuclear weapon before taking action. But for Mr. Obama, the change in wording reflects the difficult politics and logistics of acting pre-emptively against Mr. Assad. No American president has talked more about the need to prevent the use of weapons of mass destruction, and to lock down existing stockpiles. And no president has insisted more publicly that this is a time for the United States to exit wars in the Middle East, not enter new ones. "We're kind of boxed in," an administration official said this week as intelligence agencies in the United States and its allies were trying to figure out the worrisome activity at one or two of the three dozen sites where Syria's chemical weapons are stockpiled. "There's an issue of presidential credibility here," the official said. But our options are quite limited. The chief limitation, American and Israeli officials say, is that chemical weapons sites cannot be safely bombed. "That could create the exact situation we are trying to avoid," said one senior American military official, who like several others interviewed would speak only on the condition of anonymity. Making things worse, many of the storage sites are near the border with Jordan, raising the possibility that any plume of chemicals created by an attack could drift over the territory of an American ally. Putting troops on the ground has never been a serious option, American officials say. But the Israelis clearly take the concept of pre-emptive strikes seriously. They conducted one against Saddam Hussein's nuclear reactor in Iraq in 1981, and another, against a North Korean-built reactor in the Syrian desert, in September 2007. "I don't think we'd act again unless we thought Hezbollah might get their hands on these weapons," said one senior Israeli official. But we've proven that we are willing to do it, and probably more willing than the Americans. When Mr. Obama warned against moving chemical weapons, administration officials said he did not mean shifting the weapons from one site to another, which has happened several times, but preparing them for use. But in recent days, that is exactly what intelligence agencies fear has happened. American officials have detected that Syrian troops have mixed small amounts of precursor chemicals for sarin, a deadly nerve gas, at one or two storage sites - though there is no indication that Mr. Assad, whose troops are under fierce assault from rebel forces, is ready to order the use of his arsenal. Mr. Panetta said Thursday that the administration was "very concerned, very concerned" that as the opposition fighters close in on Damascus, the Syrian capital, the Assad government might actually use a chemical weapon. Over the past four decades, Syria has amassed one of the largest undeclared stockpiles of chemicals in the world, including huge supplies of mustard gas, sarin nerve agent and cyanide, according to unclassified reports by the C.I.A.