BEIRUT » U.S. support for a pair of diplomatic initiatives in Syria underscores the shifting views of how to end the civil war there and the West’s quiet retreat from its demand that the country’s president, Bashar Assad, step down immediately.

The Obama administration maintains that a lasting political solution requires Assad’s exit. But facing military stalemate, well-armed jihadists and the world’s worst humanitarian crisis, the United States is going along with international diplomatic efforts that could lead to more gradual change in Syria.

That shift comes along with other American actions that Assad’s supporters and opponents take as proof Washington now believes that if Assad is ousted, there will be nothing to check the spreading chaos and extremism. U.S. warplanes now bomb the Islamic State group’s militants inside Syria, sharing skies with Syrian jets. U.S. officials assure Assad, through Iraqi intermediaries, that Syria’s military is not their target. The United States still trains and equips Syrian insurgents, but now mainly to fight the Islamic State, not the government.

Now, the United States and other Western countries have publicly welcomed initiatives — one from the United Nations and one from Russia — that postpone any revival of the U.S.-backed Geneva framework, which called for a wholesale transfer of power to a "transitional governing body." The last Geneva talks failed a year ago amid vehement disagreement over whether that body could include Assad.

One of the new concepts is a U.N. proposal to "freeze" the fighting on the ground, first in the strategic crossroads city of Aleppo. The other is an initiative from Russia, Assad’s most powerful supporter, to try to spur talks between the warring sides in Moscow in late January. Diplomats and others briefed on the plans say one Russian vision is of power-sharing between Assad’s government and some opposition figures, and perhaps parliamentary elections that would precede any change in the presidency.

But the diplomatic proposals face serious challenges, relying on the leader of a rump state who is propped up by foreign powers and hemmed in by a growing and effective extremist force that wants to build a caliphate. Many of America’s allies in the Syrian opposition reject the plans, and there is little indication that Assad or his main allies, Russia and Iran, feel any need to compromise. The U.S.-backed Free Syrian Army is on the ropes in northern Syria, once its stronghold, and insurgents disagree among themselves over military and political strategy.

And perhaps most of all, the Islamic State controls half of Syria’s territory, though mostly desert, and it has managed to strengthen its grip even as the United States and its allies try to oust it from neighboring Iraq.

Still, Secretary of State John Kerry declared last week that the United States welcomed both initiatives. He made no call for Assad’s resignation, a notable omission for Kerry, who has typically insisted on it in public remarks. Instead, he spoke of Assad as a leader who needed to change his policies.

"It is time for President Assad, the Assad regime, to put their people first and to think about the consequences of their actions, which are attracting more and more terrorists to Syria, basically because of their efforts to remove Assad," Kerry said.

On Thursday in Geneva, Staffan de Mistura, the U.N. envoy for the crisis in Syria, also signaled a tactical shift, saying that "new factors" such as the growth of the Islamic State, also called ISIS or ISIL, must be taken into account. He said there was no point in trying to organize a third round of Geneva talks before building unambiguous support from both the Syrian government and its opponents for some kind of "Syrian political process."

The urgent search for a political solution, de Mistura said, must "bear in mind" not only the Geneva framework, "but also the need to adjust aspirations without preconditions, in line with the new factors which have come up in the reality of the area, such as ISIS."

The shifts reflect a longstanding view among U.N. officials in Syria that the West must adapt to the reality that Syrian insurgents have failed to defeat Assad. Syrians on both sides have said frequently in interviews that they fear the growing influence of foreign militants, and while they mistrust all international players that have financed warring parties, they are willing to explore compromise with other Syrians.

Western diplomats who had long called for Assad’s immediate resignation say now that while he must not indefinitely control crucial institutions like the military, a more gradual transition may be worth considering.

One Western diplomat at the United Nations said that while a "post-Assad phase" must eventually come, "the exact timing of that, we can discuss," as long as the solution does not "cement his position in power."

Western leaders now openly talk about a deal allowing some current officials to remain to prevent Syria from disintegrating, like Iraq and Libya.

"The political solution will of course include some elements of the regime because we don’t want to see the pillars of the state fall apart. We would end up with a situation like Iraq," the French foreign minister, Laurent Fabius, told a French radio station last Monday.

At the same time, such statements have further alienated Washington from ordinary anti-Assad Syrians and rank-and-file insurgents, reinforcing the idea that the West has decided to tolerate Assad.

The view that the United States supports Assad is spreading even among the groups receiving direct U.S. financing, groups deemed moderate enough to receive arms and work with a United States-run operations center in Turkey. A fighter with Harakat Hazm, one such group, said Wednesday that America was "looking for loopholes to reach a political solution and keep al-Assad."

Tarek Fares, a secular Syrian army defector who long fought with the loose-knit nationalist groups known as the Free Syrian Army but who has lately quit fighting, joked bitterly about U.S. policy one recent night in Antakya, Turkey.

"This is how the Americans talk," he said. "They say, ‘We have a red line, we will support you, we will arm you.’ They do nothing, and then after four years they tell you Assad is the best option."

The U.N. freeze proposal tries to improve on efforts over the last 18 months inside Syria, where the government and insurgents have reached local cease-fire deals to restore basic services and aid delivery — most recently on Thursday in the Waer neighborhood of the city of Homs.

But those cease-fires have never had the imprimatur of international bodies, and they often collapse. With a few exceptions they have amounted to insurgents’ surrender to a government strategy of siege and starvation.

Juliette Touma, a spokeswoman for de Mistura, said that his plan would not resemble the past cease-fires, and that the U.N., not the Syrian government, would be the guarantor. Yet even the modest Aleppo proposal is on shaky ground. While Assad has said he will consider it, his government has still not signed off on the plan; de Mistura’s deputy arrived Sunday in Damascus for consultations.

The Moscow talks are arguably in worse shape. While Kerry said he hoped the talks "could be helpful," several crucial opposition groups have refused to attend, and they say the United States has not pressured them to go.

That leaves U.S. policy ambiguous, offering only modest verbal support to the new mediation efforts while continuing to finance some Syrian insurgents — yet not enough to seriously threaten Assad. Even a new program to train them to fight the Islamic State will not field fighters until May.

Critics argue that Washington is simply trying to disengage and offload the Syria problem to Assad’s allies, Russia and Iran, even at the cost of empowering them.

Still, any attempt to bring the parties to the table should be considered constructive, another Western diplomat said. "You can’t say to the Russians, ‘Go to hell.’"

Anne Barnard and Somini Sengupta, New York Times