Mr. Obama, officials said, is now determined to put more emphasis on the “degrade” part of what the administration has said is the goal of a military strike against Syria — to “deter and degrade” Mr. Assad’s ability to use chemical weapons. That means expanding beyond the 50 or so major sites that were part of the original target list developed with French forces before Mr. Obama delayed action on Saturday to seek Congressional approval of his plan.

For the first time, the administration is talking about using American and French aircraft to conduct strikes on specific targets, in addition to ship-launched Tomahawk cruise missiles. There is a renewed push to get other NATO forces involved.

The strikes would be aimed not at the chemical stockpiles themselves — risking a potential catastrophe — but rather the military units that have stored and prepared the chemical weapons and carried the attacks against Syrian rebels, as well as the headquarters overseeing the effort, and the rockets and artillery that have launched the attacks, military officials said Thursday.