WASHINGTON -- The apparent ease with which Israel struck missile sites and, by Syrian accounts, a major military research center near Damascus in recent days has stoked debate in Washington about whether American-led airstrikes are the logical next step to cripple President Bashar al-Assad's ability to counter the rebel forces or use chemical weapons.
That option was already being debated in secret by the United States, Britain and France in the days leading to the Israeli strikes, according to American and foreign officials involved in the discussions. On Sunday, Senator John McCain, who has long advocated a much deeper American role in the Syrian civil war, argued that the Israeli attacks, at least one of which appears to have been launched from outside Syrian airspace, weakens the argument that Syria's air defense system would be a major challenge.
"The Israelis seem to be able to penetrate it fairly easily," Mr. McCain said on "Fox News Sunday." He went on to say that the United States would be capable of disabling the Syrian air defenses on the ground "with cruise missiles, cratering their runways, where all of these supplies, by the way, from Iran and Russia are coming in by air." Patriot missile batteries already installed in Turkey, he argued, could defend a safe zone to protect rebels and refugees.
The Pentagon developed such options months ago, but in recent weeks, the Joint Chiefs of Staff and Central Command, which runs military operations in the Middle East, have been asked to refine them and explore how strikes would be coordinated with allies, much as they were in the opening days of the attacks on Libya that ultimately drove Col. Muammar el-Qaddafi from power, according to several senior administration officials.
But President Obama has been reluctant to follow the course he took in that case, aides say, partly because of concerns about the strength of air defenses in Syria and partly because the opposition forces include so many jihadist elements.
So far, Mr. Obama has said he would intervene only if it turned out that Syria had used chemical weapons -- the current investigation into the use of sarin gas focuses on Aleppo and Damascus, the capital, in March -- or if such use was imminent. Now, one adviser to Mr. Obama said, "it's become pretty clear to everyone that Assad is calculating whether those weapons might save him."
The result is that the narrow goal of preventing the use of chemical weapons is beginning to merge with the broader goals of toppling Mr. Assad and seeking an end to a carnage that is already far greater than what took place in Libya, when Mr. Obama justified American intervention on humanitarian grounds.
"We have to work even harder with our allies and the opposition to accelerate Assad's exit while there is still a Syria to save," William J. Burns, the deputy secretary of state, said at a symposium at Princeton University on Saturday, as accounts of the Israeli strikes were beginning to emerge.
"There is a mounting urgency to this effort as both the human and strategic costs grow," he said. Mr. Obama, in Costa Rica on Friday, all but ruled out placing American forces into Syria, which seemed to eliminate the option of parachuting in Special Forces to secure the 15 to 20 major chemical weapons sites. That has led to a more intense examination of offshore strikes, similar to those conducted by Israel, but aimed at the delivery vehicles for chemical weapons: missiles and aircraft.
Laurent Fabius, the foreign minister of France, did not specifically address on Monday the possibility of military intervention in Syria, saying at a scheduled news conference in Hong Kong that, "There is only one solution, it is to get back to a political solution, and we French ask now to the secretary general of the United Nations, Mr. Ban Ki-moon, to be involved himself."
Mr. Fabius said France was in continuing discussions with Russia about Syria. "We are urging our American friends to be more involved" in diplomatic efforts to find a political solution, he said.
On Sunday, a senior administration official said that "there are many options short of American boots on the ground, and there hasn't been a lean in any particular direction to this point."
"If there's a decision to intervene, it's pretty darn easy to suggest airstrikes if U.S. troops aren't going to jump in to the conflict," he added. "But the reality is that any number of options -- to include airstrikes -- would probably be combined with other measures if more direct engagement is where we're heading. This isn't exactly a pick-one-from-the-menu scenario."
These issues are certain to come up on Secretary of State John Kerry's two-day visit to Moscow this week, one that Mr. Burns said would be used to argue that Russia's long allegiance to Mr. Assad is now turning against its government's interests, with a prolonged conflict only worsening the chances that the Syrian conflict will widen and promote extremism, including in the Caucasus region.
But Russia would almost certainly veto any effort to obtain United Nations Security Council authorization to take military action. So far, Mr. Obama has avoided seeking such authorization, and that is one reason that past or future use of chemical weapons could serve as a legal argument for conducting strikes, assuming they were limited to crippling Mr. Assad's ability to drop those weapons on Syrian cities.
So far among the most reluctant members of the administration to intervene heavily in Syria has been Mr. Obama himself. He declined to arm the rebels last fall, despite urging from Secretary of State Hillary Rodham Clinton and the C.I.A. director at the time, David H. Petraeus.
On Sunday, Senator Patrick J. Leahy, Democrat of Vermont, said he believed the administration was getting closer to a decision. "The idea of getting weapons in -- if we know the right people to get them, my guess is we will give them to them," Mr. Leahy said on "Meet the Press." Last week, Defense Secretary Chuck Hagel said that arming the rebels was under consideration.
In fact that debate has begun to shift in favor of more action, administration officials say. Mr. Obama's legalistic parsing of whether his "red line" for intervention was crossed when evidence arose of a limited use of sarin gas has prompted many of his allies -- led by Israeli officials -- to question the credibility of his warnings.
One administration official acknowledged late last week that the critique had "begun to sting," but said that Mr. Obama was determined to go slowly, awaiting a definitive intelligence report on who was responsible for the presence of sarin before deciding on a next step.
Keith Bradsher contributed reporting from Hong Kong.
This article originally appeared in The New York Times.