The Pentagon estimates it would need 75,000 troops to secure Syria's chemical weapons sites, according to the New York Times:
The Pentagon has not yet been directed to draft detailed plans of how it could carry out such a mission, according to military officials. There are also contingency plans, officials say, for securing a more limited number of the Syrian chemical weapons depots, requiring fewer troops.
The discovery that Hezbollah has set up camps close to some of the depots, however, has renewed concern that as the chaos in Syria deepens, the country’s huge chemical weapons stockpiles could fall into the wrong hands. Hezbollah fighters have been training at “a limited number of these sites,” said one senior American official who has been briefed on the intelligence reports and spoke on the condition of anonymity. “But the fear these weapons could fall into the wrong hands is our greatest concern.”