“We should try to help the rebels and help the people fighting Assad,” Mr. Engel said.

Frederic C. Hof, a senior fellow at the Atlantic Council who previously worked on Middle East issues for the State and Defense Departments, has urged that the Obama administration consider a broader military mission: destroying or significantly degrading the ability of the Assad government to carry out intensive artillery, aircraft and rocket attacks with conventional as well as chemical warheads on the civilian population.

“Something that is significantly less than that, something that is seen as symbolic, I think would just enable Bashar al-Assad to say I have stood up to the world’s only superpower and faced it down,” he said.

The main American attack is expected to be carried out by cruise missiles from some or all of the four Arleigh Burke-class destroyers within striking range of Syria in the Mediterranean: the Mahan, the Barry, the Gravely and the Ramage.

Each ship carries about two dozen Tomahawk cruise missiles, a low-flying, highly accurate weapon that can be launched from safe distances of up to about 1,000 miles. Tomahawks were used to open the conflicts in Afghanistan in 2001, in Iraq in 2003 and in Libya in 2011. Attack submarines also carry Tomahawks and are assumed to be on station in the Mediterranean as well.

Officials said that while Syrian rocket and artillery sites were expected to be targeted, there were no current plans to use Tomahawks to crater airfields used by the government to receive weapons and military supplies from Iran, an important lifeline for the Assad government.

Weapons experts said that Tomahawk missile strikes, while politically and psychologically significant, could have a limited tactical effect. The weapons are largely fuel and guidance systems and carry relatively small high-explosive warheads. One conventional version contains about 260 pounds of explosives and another version carries about 370 pounds. Each is less than the explosive power of a single 1,000-pound air-dropped bomb.

The weapons are not often effective against mobile targets, like missile launchers, and cannot be used to attack underground bunkers. Naval officers and attack planners concede that the elevation of the missile cannot entirely be controlled and that there is a risk of civilian casualties when they fly slightly high.