The New York Times reports: With the growing conviction that the Assad family’s 42-year grip on power in Syria is coming to an end, Obama administration officials worked on contingency plans Wednesday for a collapse of the Syrian government, focusing particularly on the chemical weapons that Syria is thought to possess and that President Bashir al-Assad could try to use on opposition forces and civilians.

Pentagon officials were in talks with Israeli defense officials about whether Israel might move to destroy Syrian weapons facilities, two administration official said. The administration is not advocating such an attack, the American officials said, because of the risk that it would give Mr. Assad an opportunity to rally support against Israeli interference.

President Obama’s national security adviser, Thomas Donilon, was in Israel over the weekend and discussed the Syrian crisis with officials there, a White House official said.

Mr. Obama called President Vladimir V. Putin of Russia on Wednesday and urged him again to allow Mr. Assad to be pushed from power. Russia, so far, has refused. A White House statement said that Mr. Putin and Mr. Obama “noted the growing violence in Syria and agreed on the need to support a political transition as soon as possible that achieves our shared goal of ending the violence and avoiding a further deterioration of the situation.”

The statement pointedly noted the “differences our governments have had on Syria,” but said the two leaders “agreed to have their teams continue to work toward a solution.”

American diplomatic and military officials said the bombing in Damascus on Wednesday that killed several of Mr. Assad’s closest advisers was a turning point in the conflict. “Assad is a spent force in terms of history,” Jay Carney, the White House press secretary, told reporters. “He will not be a part of Syria’s future.”

Alluding to Russia’s position, Mr. Carney said the argument that Mr. Assad’s ouster would result in more violence was refuted by the bombing, and that Mr. Assad’s continued rule “will result in greater violence,” not less.