Still, the consequences of a U.S. strike could be complex: the Assad regime could intensify its assault on outgunned rebels; Iran or Hezbollah could launch attacks on Israeli or Western targets; or al-Qaeda or other jihadist fighters could exploit a moment of government weakness to gain new ground.
Separately, rebels might be tempted to exaggerate any more limited use of chemical agents by the Syrian government in the future, or even to stage further attacks and blame the regime, just as Syria and Russia have accused them of doing in the Aug. 21 attack that sparked international outrage.
Russia may broaden its weapons supply to Assad and pull back from plans to work alongside the United States to settle the Syrian conflict peacefully. Iran may use the attack as pretext to refuse any negotiation over its disputed nuclear program.
Several analysts said that the most likely outcome is that there is little discernible reaction, at least not right away.
“What does the day after look like? We’re likely to see something from a very limited response within the region to maybe nothing at all,” said security analyst Mark Jacobson of the German Marshall Fund of the United States.
In every case, the nations with the most reason to retaliate also have bigger problems or longer-term aims that argue against getting into a tit-for-tat with the United States, analysts and diplomats said.
“All of the main actors have stronger incentives not to respond with violence than to do so,” said Kenneth Pollack, a Middle East analyst at the Brookings Institution.
“The Iranians have their hands full,” in Syria and at home, Pollack said. “They are not looking for a fight -- not with us, not with the Israelis, not with the other Arabs.”
President Obama said Friday he has not yet made a final decision on a military strike, but is considering only a “limited, narrow act.”
Secretary of State John F. Kerry said Friday that any U.S. response is intended to be heard well outside Syria — anywhere that leaders or terrorist networks might want to test U.S. resolve if the Assad attacks go unanswered.
“It is about whether Iran, which itself has been a victim of chemical weapons attacks, will now feel emboldened, in the absence of action, to obtain nuclear weapons,” Kerry said. “It is about Hezbollah, and North Korea, and every other terrorist group or dictator that might ever again contemplate the use of weapons of mass destruction.”
A senior administration official said the planning includes consideration of possible implications for U.S. personnel and U.S. interests in the region.