BEIRUT, Lebanon -- As President Bashar al-Assad of Syria faces the increasing likelihood of an American-led missile strike, his detractors and defenders alike are asking, Why would he launch a deadly chemical attack on a scale not yet seen in his country's civil war -- as American and allied officials assert his loyalists did last week -- when he seemed to be holding his own in the stalemated conflict, and just as international weapons inspectors arrived in the country?
Mr. Assad's allies have tried to cast doubt on the allegations by saying there would have been no logical benefit for his government in launching the attack. And even some of those advocating a military response have expressed puzzlement over why he would take one of the few actions that could push a reluctant American government to respond.
If the Syrian government is responsible for the attack, which it denies, the reasons for it are known only to Mr. Assad's inner circle. But military analysts say that he and his loyalists may have had ample reasons that made sense to them: further terrorizing rebel supporters, projecting confidence by defying the international community, or simply wanting to raise the military pressure on some of the most stubborn and strategic pockets of rebel fighters and their backers.
"What makes military and strategic sense to Assad may not make military and strategic sense to us," said Emile Hokayem, a military analyst at the International Institute for Strategic Studies. "Assad is fighting his own fight on his terms and on the timing of his choosing. He may have made a mistake this time -- perhaps he didn't mean to kill that many, or assumed the international community had become less sensitive -- but it doesn't mean that it didn't make sense from his perspective."
The attack, which killed hundreds of people in heavily bombarded suburbs east and southwest of Damascus, the capital, appears to have been by far the most widespread and deadliest use of chemical weapons in Syria, where toxic gases have been used in several smaller attacks over the past year, with each side accusing the other of using the internationally banned weapons.
Yet in some ways, the episode may represent more of a continuity with the conduct of this war than a departure from it. During two and a half years of conflict, Mr. Assad has slowly increased the intensity of attacks on civilian neighborhoods where rebels have found support. Mr. Hokayem calls it a strategy of "gradual escalation and desensitization" of the public in Syria and abroad.
Government forces have used blunt and imprecise conventional weapons, firing Scud missiles and unleashing artillery bombardments and airstrikes on neighborhoods, in attacks that seem aimed more at sowing fear and punishing populations than at specific tactical gains. While last week's killings appear to have been the largest mass slaughter of the war, conventional weapons have killed many times more people than chemicals.
Even after Western governments declared that Syrian government forces had used banned chemical weapons like the nerve agent sarin, crossing what President Obama had once called a "red line," the attacks provoked little visible response.
And in recent weeks, with the United States and its allies increasingly queasy about Islamic extremists among Mr. Assad's fractious opponents and the prospect that his fall would bring even greater chaos to the country and the region, Mr. Assad could watch Egypt's generals preside over the killing of more than 1,000 Islamist protesters, also with few international repercussions.
Some analysts say that a growing sense of impunity may have led Mr. Assad to believe that he could get away with an attack much larger than past ones. Others say they suspect that he intended only an incremental increase in the use of chemicals and that a tactical error led to last week's much higher death toll, and to the pictures of children's bodies shrouded in white that provoked a new level of international outrage.
On the eve of last Wednesday's attack, Mr. Assad's forces had consolidated gains around the central city of Homs, aiming to secure the heavily populated corridor running from Damascus through the government's coastal strongholds to the divided northern city of Aleppo. But the capital remained ringed by restive suburbs where by some estimates half the population stayed despite relentless shelling, and where the government has been unable to decisively dislodge rebels.
Yezid Sayigh, an analyst of Arab militaries at the Carnegie Middle East Center in Beirut, said government forces have used chemical weapons in small amounts several times to incapacitate fighters on front lines as it tries to take specific areas, and could have been trying to do so on a somewhat larger scale in last week's attack.
The government, Mr. Sayigh said, may also have sought to use the psychological effect of chemical weapons to frighten away residents who had stayed until then, to deny rebels cover and support and to add new refugee flows to those already burdening Syria's neighbors.
"They clearly felt a need to use chemical weapons quite a while ago and were able to get away with that, bluntly, as long as they kept it within certain limits," he said. "Maybe they felt they needed to achieve significant progress in the Damascus area, and loosened the rules of engagement."
Although it might seem strange to use chemical weapons during a visit by United Nations weapons inspectors, the deterrent effect of international observers has been overestimated in the past, said Mr. Hokayem of the strategic studies institute, noting that some of the first large-scale massacres in the conflict took place during a visit by United Nations observers.
Analysts said the possibility that the attack was by a rogue commander seemed remote, as did the idea that the attack was desperate and irrational.
The security forces have remained relatively cohesive and organized. The government has scaled back its military goals, recognizing that it cannot fight everywhere at once, but it displays a greater ability than the rebels to systematically make decisions about allocating resources and weapons to areas it considers important at a particular time.
Still, the government is not monolithic. There are different power centers within its security forces, and some analysts have speculated that Mr. Assad's brother Maher, the leader of the feared Republican Guard, could have given the order, or that it was carried out by irregular forces. Evidence from videos and witnesses suggested that the toxic substances in last week's attack were delivered by improvised tube-launched missiles that could be used by smaller, more mobile units than were thought to be needed for chemical weapons.
Syria's allies Russia and Iran have said the attack was carried out by rebels, who produce many homemade weapons. But the government has also used seemingly improvised weapons in conjunction with standard ones, as when its forces dropped barrel bombs from helicopters.
Mr. Sayigh of the Carnegie Middle East Center noted that the Syrian government was accused of similar miscalculations in the past, like taking a tacit or active role in the assassination of Lebanon's former prime minister, Rafik Hariri, in 2005 -- an event that led to Syria's withdrawal of its occupying forces from Lebanon under pressure.
"They are used to acting in blunt ways," he said. "Now and then they miscalculate."
C. J. Chivers contributed reporting from the United States.
This article originally appeared in The New York Times.