He said that for the current news reports to make sense, Syria’s chemical weapons capability would have to be as crude as, or cruder than, Iraq’s in the 1990s, when, he said, the Iraqi mixing process consisted of “Jeeps with bomb trailers driving around the airfield to mix the two final precursors.” He noted that Iraq did not mix its chemicals in advance. “The mixing was done literally minutes before the bombs were loaded onto the planes,” he said – a sequence that obviously has not happened in Syria.

One top international chemical weapons official, who spoke on condition of anonymity because he’s involved in diplomacy on the issue, said he feared that news reports on the disposition of Syria’s chemical weapons are based on a few pieces of reliable information that have been repeated again and again, amplifying the threat each time.

“The evidence that exists of chemical weapons in Syria is very widespread and very authoritative, but there is a circularity about how this information moves around in the media sphere,” the official said.

So far, the official said, evidence suggests that the Syrian regime is storing sarin gas in “binary form,” meaning the components are being kept separately and therefore safely. If credible evidence surfaces that shows the regime mixing the components, “that’s an entirely different story,” the official said, but quickly added that “it’s very difficult to envision a reason they’d do this.”

Gregory D. Koblentz, an expert on chemical terrorism for the Council on Foreign Relations in Washington, noted that there are tactical reasons not to use chemical weapons in a civil war.

With battle lines fluid and supporters and enemies occupying almost the same space, deploying chemical weapons runs the risk of a disastrous backfire if, say, the wind shifts or an engine misfires. Tactically, when Iraq used chemical weapons against Iran, the weapons were used before an offensive, to weaken the resolve of Iranian fighters. And when Iraq used the weapons against the Kurds, they were dropped into northern regions where there was no Iraqi military presence.

Barring clearly defined battle lines, such as a national border, a military commander would have reservations about using chemical weapons.

“They have a limited utility,” Koblentz said. “And they can mess up your own operations.”

Experts agreed that the greatest threat regarding Syria’s chemical weapons comes not from the Assad regime but from the Islamist radicals, including some with alleged links to al Qaida, who are at the forefront of the rebel fighting force. The experts are urging U.S. officials to work closely with the rebels to ensure the security of chemical weapons depots in contested areas, recommending that the rebels make clear that Syrian soldiers charged with guarding those facilities be allowed to remain on duty with assurances that they won’t face retaliation and could be rewarded by a post-Assad government.

Leonard S. Spector, director of the James Martin Center for Nonproliferation Studies in Washington, and Egle Murauskaite, a research associate at the center, put forth those and other suggestions in a grim report on Syria’s chemical weapons for last month’s issue of Arms Control Today. They added that, should the sites come under insurgent control, the rebels should be pressed to authorize inspections by international experts and should be reassured that the successful prevention of weapons falling into the wrong hands could be rewarded with foreign aid.

The two warned in the paper, however, that the international community should remain skeptical as the rebels sound alarms about the Assad regime’s willingness to resort to chemical weapons.

“The political reasons behind recent rebel rhetoric on chemical weapons must be acknowledged,” Spector and Murauskaite wrote. “Knowing that the international community regards the issue . . . as a potential trigger for intervention, the rebels may be inclined to place particular emphasis on that issue in their rhetoric in the hopes of keeping international attention focused on their plight.”

Thielmann, the former State Department arms control official, said the Obama administration faces “a policy conundrum,” because there are no appealing options for safeguarding Syria’s weapons. Such weapons can’t be destroyed in an airstrike without the likelihood of setting them off, the exact result the airstrike would be intended to avoid.

They also can’t be seized in a ground operation without risking that Assad will actually use them. A Syrian Foreign Ministry official said recently that Syria’s chemical weapons were reserved solely for an external threat, such as foreign troops entering the country, and would not be used against Syrians.

Jonathan S. Landay contributed to this report.