In this July, 2015 file photo, a fighter from the Free Syrian Army' walks towards his position on the front line against the forces of Syria's President Bashar al-Assad in a suburb of Damascus. (Bassam Khabieh/Reuters)

Administration decisions on a series of proposed adjustments to its strategy against the Islamic State have been put on hold pending more information about Russia’s intentions in Syria and President Obama’s desire for clarification of the proposals themselves, according to senior administration officials.

Even as Russian President Vladi­mir Putin started sending tanks, aircraft and additional personnel to Syria’s Mediterranean coast early this month, Obama told his top national security advisers to step back and assemble a sharper picture of how various proposed initiatives would fit together into a coherent whole and improve what is a largely stagnant conflict.

Putin’s moves have further delayed and complicated decision-making on plans that include sending U.S. arms directly to Kurdish and Arab rebels in northeastern Syria, and scaling back and revamping a failed U.S. military training program for other Syrian opposition fighters.

The Russian leader’s objectives remain a mystery to the White House, leading Obama to conclude that the best way to find out is to ask him directly. The two are scheduled to hold a formal meeting for the first time in two years on Monday, after they both deliver morning speeches at the U.N. General Assembly.

For now, officials said, Obama’s goal is to hear Putin out, to stress U.S. policy goals and warn against interference, and to determine whether there is room for cooperation.

Obama will also take advantage of the U.N. gathering to hold a Tuesday summit of the anti-Islamic State coalition and other counterterrorism partners, while Secretary of State John F. Kerry holds individual meetings with his coalition counterparts to go over the new proposals, the administration’s take on Putin’s game plan, and the growing Syrian refu­gee crisis.

What appears certain is that the preferred U.S. outcome — Moscow’s agreement to support a political negotiation among Syrians including the early departure of Syrian President Bashar al-Assad, a Russian client — is not what Putin has in mind.

As Syria’s chaotic, multi-front and multi-player war has expanded, the administration itself now appears to have softened its terms for Assad’s departure. While Assad still must go, Kerry said a week ago in London, “it doesn’t have to be on Day One or month one or whatever.”

Kerry’s words, officials said, reflect long-held fears that the collapse of Syrian institutions would lead to a void into which militants could expand even further, as they did in Iraq a decade ago, following the U.S.-engendered collapse of the Iraqi army.

Russia and Iran, Assad’s other principal ally, have repeatedly countered U.S. insistence that ­Assad must negotiate his own demise by asking what political alternative Washington proposes. It is, officials acknowledged, a difficult question to answer given the ongoing failure to establish a viable political opposition among U.S.-backed Syrian moderates.

Several officials spoke on the condition of anonymity to discuss the current state of administration decision-making on Syria, the Islamic State and Russia.

Russia’s stated purpose for its new Syria deployments is to contribute to the fight against the Islamic State. If that means joining the United States in airstrikes, there is room for both to operate without running into each other. U.S. strikes are focused on control of the Syria-Turkey border, on the north-central city of Raqqa that is the militants’ de facto capital, and on Islamic State supply lines through eastern Syria into Iraq.

In recent months, the militants have taken over new pockets in central and western Syria that are contested by no other force.

For now, as Russian fighter jets are positioned on the ground with no indication of how they will be used, the United States has stressed the need for “de-confliction” to avoid potential future problems of operating in the same or nearby battle spaces.

Officials have speculated that Putin wants to distract Western attention from Ukraine, where Russian and separatist forces remain in control of the eastern border and substantial territory, and where U.S. and European sanctions are due to be renewed or expanded if there is no progress in the coming months.

Another possibility is that Moscow may want to help Assad establish firmer control over what could become a rump Syrian state in western population centers and the Mediterranean coast. In these areas, Assad’s forces are fighting against a mixture of U.S.-backed opposition forces and non-Islamic State extremists, including Jabhat al-Nusra, al-Qaeda’s Syrian affiliate. Preservation of this territory under the current government would also preserve long-term Russian military equities, including a naval base.

A Russian decision to launch air attacks against Jabhat al-Nusra and other groups that the United States considers terrorist organizations would present a quandary for the administration, particularly if Russian forces displayed the same disregard for civilian casualties as Assad’s.

As the administration awaits further clarification of Russian aims, the State Department and Pentagon are formulating and fine-tuning proposed strategy adjustments in the anti-Islamic State campaign in both Syria and Iraq. In the past, they have frequently been at odds over how to execute the strategy, with State advocating a more muscular approach and the military urging more caution.

One of the new variables in the strategy equation is a change of leadership on both sides. Gen. Martin E. Dempsey retired Friday as chairman of the Joint Chiefs of Staff and Obama’s chief military adviser, replaced by Marine Gen. Joseph F. Dunford, who served until last month as commander of the U.S. and international force in Afghanistan. The State Department’s special envoy to the ­anti-Islamic State coalition, retired Gen. John Allen, who was known to have been frustrated by the Pentagon’s reticence, is due to leave that job this fall.

Administration officials have heavily touted this summer’s success of Syrian Kurds and a smaller force of Syrian Arabs in driving Islamic State forces from much of the Turkish border between Iraq and the Euphrates River. The hope is that those forces, aided by U.S. airstrikes, will now begin to move southward toward Raqqa.

But Syrian Kurdish leaders say they are in desperate need of supplies, which the United States has so far declined to provide directly. A decision to do so — effectively opening up a land bridge from neighboring Iraq in the east — would require Obama to sign off on a change in U.S. vetting procedures for the recipients of U.S. weapons and ammunition in Syria.

The advisability of that plan was thrown into question Friday by the Pentagon’s acknowledgment that pickup trucks and ammunition provided to a separate group of vetted Syrian fighters, trained by the U.S. military and called the New Syrian Force, had been turned over to Jabhat al-Nusra.

The $500 million training program, designed to insert thousands of fighters to combat the Islamic State on the other side of Syria from the west along the Turkish border, has been fraught with problems. From the start, the military had trouble recruiting and vetting Syrians who were interested in fighting against the Islamic State, rather than against Assad. After nine months, Gen. Lloyd J. Austin III, head of the U.S. Central Command, said two weeks ago that only “four or five” had been successfully inserted into Syria.

The Central Command has formulated new plans for the train-and-equip program that would jettison the idea of establishing a new fighting force. Instead, the training would focus on smaller numbers and more specific tasks, including forward air spotters who could be melded with U.S.-backed forces such as the Kurds, to coordinate airstrikes against the Islamic State.