NEW YORK - The United States is engaged in extensive planning and preparations for a post-President Bashar al-Assad Syria, hoping for a smooth transition in the event the rebel militias topple the regime, according to a media report.

In a dispatch, The New York Times said, “the State Department and Pentagon are quietly sharpening plans to cope with a flood of refugees, help maintain basic health and municipal services, restart a shattered economy and avoid a security vacuum in the wake of Assad’s fall.”

Citing administration officials, the newspaper said both agencies have created a number of cells to draft plans for what many officials expect to be a chaotic, violent aftermath that could spread instability over Syria’s borders, even though no official could predict whether Assad’s demise was weeks or months away.

The State Department is considering positioning additional food and medical supplies in the region and is studying how to dismantle the raft of American and European sanctions against Syria quickly to allow investment to flow in and business to resume, avoiding further deterioration of life for ordinary people, the report said.

“It is also pressing the opposition in Syria to avoid harsh retaliation against the army, the police and the municipal agencies of Mr. Assad’s government that could cause a security vacuum and a collapse of services. Looting and chaos after the overthrow of Saddam Hussein in Iraq in 2003 planted the seeds of a lasting insurgency,” the report said.

“We don’t want them to dissolve all the institutions in place,” an administration official said, was quoted as saying on the condition of anonymity to discuss planning that is largely being conducted out of public view.

“Even though the White House has all but ruled out military intervention, the Pentagon is drafting contingency plans for operations with NATO or regional allies to manage a large flow of refugees over Syria’s borders and safeguard the country’s arsenal of chemical weapons,” the dispatch said.

“The administration’s efforts have been driven by a bleak prognosis shared by most officials: Mr. Assad’s fall would be likely to set off a grave, potentially violent and unpredictable implosion in a country strained by even more tribal, ethnic and sectarian divisions than Iraq, possibly in the midst of a presidential election campaign at home”.

“The main question we’re looking at is how it all plays out after the Assad regime collapses,” one American official was quoted as saying by the Times.  “Chapter 1 is he’s gone. Chapter 2 is the post-Assad transition, and initial efforts at stabilization. Chapter 3 is completely unknown, and therefore more than a little scary.”

Rafif Jouejati, an American of Syrian ancestry who is a spokeswoman for a network of activists in Syria, was cited as saying that those committed to Assad’s removal had no interest in “a foreign transition plan,” however well intentioned.

“What we don’t want to do is descend into the total chaos that Iraq did,” said Ms. Jouejati, who is participating in a similar planning effort among Syrian activists coordinated through the United States Institute of Peace, a Congressionally financed organization in Washington. Even so, she added, “I don’t think we want the United States to impose lessons learned here.”

The State Department and Pentagon planning efforts became more “systematic” last month after hopes for an internationally brokered resolution faltered in the face of Russian and Chinese opposition in the United Nations Security Council, the report said. The planning is being closely coordinated with regional allies like Turkey, Jordan and Israel, and it coincides with an expansion of overt and covert American and foreign assistance to Syria’s increasingly potent rebel fighters.

While the administration has ruled out arming the rebels directly, the report said, the administration has authorized $25 million in direct assistance for medical supplies and communication equipment to help the fighters and civilian opponents of Assad coordinate their activities and, crucially, disseminate reports about the fighting to the rest of the world.

Other countries, including Turkey, Saudi Arabia and Qatar, are providing weapons, assisted by a “small number of officers” from CIA who are vetting the fighters receiving them and working with State Department officials trying to unify the fighters with political leaders inside and outside the country. Last month, the Treasury Department granted a waiver to let a new American organization, the Syrian Support Group, raise money for the rebels despite the sanctions that prohibit most financial transactions in Syria.

On Thursday, President Obama also announced a $12 million increase in humanitarian aid, bringing the total to $76 million, largely distributed through international organizations like the World Food Programme.

The State Department effort is being coordinated by Deputy Secretary of State William Burns, who worked in the Near Eastern Affairs Bureau during the planning for the American invasion of Iraq in 2003, when the department clashed with the Pentagon over what to do after Saddam Hussein’s fall. The department has created a number of separate cells devoted to aspects of a post-Assad Syria, including humanitarian issues, economic reconstruction, security, the stockpiles of chemical weapons and a political transition.

The last is led by the American ambassador to Syria, Robert Ford, who closed the embassy in Damascus in February amid deteriorating security there and is now based in Washington. Ford met in Cairo last week with more than 250 Syrians to shape plans for the inchoate opposition groups to form a transitional government. That meeting followed a larger gathering of Mr. Assad’s opponents last month, organized by the Arab League.

The Pentagon, along with Central Command, has established a similar group of planning cells, known as “crisis action teams,” focused on contingencies that could involve the American military. Senior officials declined to give the number and emphasized that such cells are created whenever potential crises emerge, the report said.

The range of plans being drafted, however, underscored the gravity of the risks. Atop the list is protecting Syria’s chemical weapons, which its leaders acknowledged possessing when vowing last month to use them only in the event of a foreign invasion. “That would be a purely military-type mission, and so we have to think about contingency planning for safeguarding these stockpiles,” one official said.