In recent meetings, South Korean officials told their U.S. counterparts that continued White House inaction in Syria could embolden North Korea to use its own chemical weapons against its southern neighbor.
Similar messages were relayed by Turkish, Israeli and Saudi officials in recent days, telling President Barack Obama he must respond to Syria's alleged use of chemical weapons, current and former U.S. and Middle Eastern officials said. Failure to act, these allies said, could convince Iran that Washington isn't serious about halting its pursuit of nuclear weapons.
Mr. Obama's possible move to strike Syria is designed to retaliate against Syrian President Bashar al-Assad for what the U.S. and others call a chemical-weapons attack on Aug. 21. A strike would also be intended to persuade friends and foes alike that the U.S. won't renege on global-security commitments.
Current and former U.S. officials say growing concerns about American credibility helped tip the scales within the White House in favor of a limited military intervention. Two months ago, when U.S. intelligence agencies concluded that Mr. Assad had crossed Mr. Obama's "red line" by using chemical weapons on a smaller scale, neither the president nor his top military advisers favored striking Syria.
Some Middle Eastern diplomats and American lawmakers have lamented the limited nature of Mr. Obama's telegraphed intervention in Syria, saying only more decisive action might be enough to deter such countries as Iran, North Korea, Russia and China from bucking U.S. interests. Indeed, Mr. Assad already has taken advantage of a week of U.S. saber-rattling to disperse military equipment and forces where it will be harder to destroy them with a limited number of strikes, U.S. officials said. The Pentagon is adjusting its targeting in response, a senior official said.
U.S. military action against Syria likely would join a growing list of instances in which the U.S. has fired Tomahawk cruise missiles.
In a conference call on Thursday to brief lawmakers on U.S. intelligence, Defense Secretary Chuck Hagel, who was traveling at the time in Asia, said that South Korean leaders were concerned that U.S. inaction in Syria would make North Korea think it could get away with using chemical and biological weapons without consequence.
Mr. Kerry made explicit that argument during formal comments Friday on Syria, when he said the choice facing the administration was "directly related to our credibility and whether countries still believe the United States when it says something." He said not acting would mean there would be "no end to the test of our resolve" from countries who think they can act with impunity.
That the U.S. felt the need to reassure allies about its commitments is partly a consequence of Mr. Obama's deliberately light footprint on the world stage. A hallmark of Mr. Obama's foreign policy has been a concerted effort to lower expectations that the U.S. would automatically assume the role of global policeman, given the president's preference to concentrating on his domestic policy agenda, officials and experts say.
Events overseas, however, notably the Arab Spring and its bloody aftermath, have time and again pulled the administration back to a region from which Mr. Obama wanted to withdraw.
Sen. John McCain (R., Ariz) described the Obama Syria policy as "muddled," citing Mr. Obama's past assertions that Mr. Assad should step down. "So the president two years ago said he had to leave power, but now that [Mr. Assad] has committed a war crime, the president of the United States says he's not interested in removing him from power."
Colin Kahl, a former Obama administration Pentagon official, said the president's expected military action was an appropriate demonstration of U.S. credibility. "One of the things I heard most often when I was in the administration is that superpowers don't bluff," he said. "That's why the administration has been very cautious across a whole host of issues not to issue a lot of red lines."
In the run-up to the strikes, Mr. Obama suffered a series of embarrassing international affronts, which underlined the limits of U.S. influence.
Hong Kong then Russia refused to hand over National Security Agency leaker Edward Snowden to the U.S. In July, Egyptian generals with long-standing ties to the Pentagon overthrew their country's first democratically elected president over U.S. objections. The U.S. subsequently saw its message to Cairo undercut by Saudi Arabia, the United Arab Emirates and Israel, its closest regional allies, which urged the generals to crack down hard on the Muslim Brotherhood over Washington's warnings.
The Obama administration also struggled to bring allies on board this week, notably the U.K., whose parliament scotched the prospect of a joint mission.
The administration has long been divided over how to tackle Mr. Assad's forces. Even before the alleged chemical-weapons attack, Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, cautioned the White House against trying to change the balance of power, citing a danger that opposition groups linked to al Qaeda will try to gain the upper hand. Officials say Gen. Dempsey backs the limited strikes now on the table, citing the importance of U.S. credibility and about sending a message that chemical-weapons use won't be tolerated.
At the direction of the State Department this week, ambassadors in the Middle East have been prodding Arab leaders to issue statements of support for the U.S., but the early results haven't been encouraging, officials in the region say.
Besides Mr. Assad, U.S. allies and foes remain a target audience for the pending military action. One former administration official said the South Koreans and the Israelis "have been beating this drum hard" in talks with the U.S. and its allies, questioning the U.S.'s security commitments to defend them against North Korea and Iran.
Israel, on the border with Syria, is one of the U.S.'s biggest concerns. The Israelis are worried that Lebanese militant group Hezbollah could be encouraged by U.S. inaction to acquire sophisticated guided rockets that could be loaded with poison gas. If Israel is attacked by either Syria or Hezbollah, Israeli have made clear they will respond with force.
The U.S. has sought to reassure Israel that Mr. Obama will enforce U.S. "red lines" with Tehran, going so far as to show top Israeli officials a secret Pentagon video showing what the largest U.S. bunker buster bomb can do. Israeli leaders remain skeptical of Mr. Obama's intentions, reflected in efforts by the Jewish state to build a bunker buster of its own, according to American and Israeli officials.
Saudi King Abdullah, meanwhile, has sent private messages to Mr. Obama warning the American president that an abdication of U.S.'s leadership would have dire consequences for U.S. allies in the Middle East, according to U.S. officials.
"Your credibility is on the line, not just in the region but globally," he warned Mr. Obama in one of those messages, according to U.S. officials briefed on the exchange.
—Peter Nicholas contributed to this article.
A version of this article appeared August 30, 2013, on page A1 in the U.S. edition of The Wall Street Journal, with the headline: Quietly, Some Allies Push for Action.