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.
“We’re talking to our international partners who have a stake,” said the official, who requested anonymity because the decision to attack is not final.
Iran’s disputed nuclear program is likely to figure in its decision about how to respond to any U.S. strike on its ally, but maybe not the way Kerry outlined, diplomats and analysts said. Retaliating either directly or indirectly on Assad’s behalf could invite the same kind of strike against its nuclear facilities, Pollack said. Obama drew two red lines in the Middle East — one against Syrian use of chemical weapons and one against an Iranian nuclear bomb.
“The more they start mixing it up with us the more the odds go up,” of a unilateral American strike on Iranian facilities, Pollack said.
Jacobson agrees Iran is likely to take the long view. Hezbollah, he said, has its hands full already in Lebanon and Syria, and letting loose Iranian proxies against American targets risks making those proxies more of a target for the United States.
“I think the technical term is schwacked,” he said.
Syria has pledged to defend itself, but Assad and his backers may be more likely to try to use the attack to garner sympathy than to mount widespread military retaliation beyond Syrian borders, defense and diplomatic analysts said.
“President Assad might dismissively belittle any strike or turn it to his advantage in a local and regional PR offensive, that embarrasses his Arab adversaries,” said Daniel Levy, director of the Mideast program at the European Council on Foreign Relations in London.
The likely targets for a brief military strike are intended to reduce Assad’s ability to launch future chemical attacks but do not appear to give the rebels much, if any, military advantage in their conventional fight with regime forces.
Israel expects that Assad’s government will survive the attack intact. While prepared for a possible retaliatory strike from Iran or Syria, the Israeli assessment is that it will not happen. Israel assesses that Hezbollah will be reluctant to risk a strong Israeli counterstrike if it uses the opportunity of a U.S. attack on Syria to strike Israel beyond the occasional rocket.
Russian reaction is expected to be largely rhetorical. Foreign Minister Sergei Lavrov this week denounced any potential Western attack as misguided and shortsighted, but added that Russia will not “go to war with anybody,” as a result.
Other Russian officials have warned that Washington is recklessly inviting a militant surge.
“The West behaves toward the Islamic world like a monkey with a grenade,” Russian Deputy Prime Minister Dmitry Rogozin tweeted Wednesday.
State Department spokeswoman Marie Harf did not directly respond when asked whether the administration is concerned about stirring up militancy.
“As we determine and decide and debate what steps will be taken in response to this attack, clearly there are a variety of factors that go into that determination: possible unintended consequences, possible effects in the region,” Harf said Wednesday.
Sen. Lindsey Graham (R-S.C.) said in a briefing for key lawmakers Thursday, Kerry the United States would be an international “laughingstock” if it left the use of chemical weapons unanswered, and that officials cited potential threats from Iran and North Korea if there was no U. S. response.
But Graham said he heard no larger strategy or plan for ending the violence in Syria or addressing larger issues of militancy in the Middle East.
“It’s a persuasive case, and I want to help the president where I can but this is a disjointed response,” Graham said.
Karen DeYoung contributed to this report.