The United States and its principal European and Arab allies have agreed on a unified way of providing Syrian rebel groups with aid, classifying them into those who should receive arms supplies and other assistance, those who are ineligible because of clear extremist ties, and those whose eligibility requires further discussion, according to U.S. and allied officials.

Along with new initiatives by the United States and others to increase weapons shipments, rebel training, intelligence and other support, the plan — set during a U.S.-led meeting of intelligence chiefs here last week — is designed to overcome divisions among governments that have been deeply split over which opposition groups to aid and what to supply.

“The idea is that no country will act unilaterally and all will abide by the same understanding,” said one Arab official. The official called the listing a “living document” that will be constantly updated as rebel alliances shift.

It is far from the first effort to organize outside assistance over the past two years of Syria’s grueling civil war. Turkey, Qatar, Saudi Arabia, France and the United States, among those who participated in last week’s meeting, have often disagreed over how to bolster the opposition and undermine Syrian President Bashar al-Assad.

But officials from several European and Arab governments represented at the intelligence gathering and at other high-level U.S. meetings in recent weeks — many of whom have complained in the past about a lack of administration leadership — said there has been a substantive shift toward a more aggressive U.S. posture and a willingness by others to follow that lead.

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While foreign officials praised a new administration sense of “urgency,” U.S. officials hailed a new level of cooperation from the foreigners.

All, however, attributed the change to the same factors. Among them are growing fissures in rebel ranks that have allowed a clearer evaluation of which are considered moderate enough to aid.

“We’re seeking to take advantage of the divisions that have emerged in the opposition,” a senior administration official said, pointing in particular to splits between the extremist Islamic State in Iraq and Syria and other groups. “I think that has helped us have a more constructive conversation with . . . [Persian] Gulf states and the Turks and some Europeans about how do we focus our assistance with a common set of actors.” Officials spoke on the condition of anonymity about intelligence matters.

It was unclear whether the reassessment would cause the administration to move beyond its policy of aiding only the Free Syrian Army or if it was focused primarily on administration hopes that others would stop aiding those it sees as extremists.

U.S. and European attention in Syria has increasingly focused on a spillover of the war far beyond the Middle East. New intelligence assessments have warned of growing numbers of foreigners within the extremists’ ranks, including hundreds of Europeans whose passports allow them to enter this country without visas.

In congressional testimony late last month, senior U.S. intelligence officials compared some rebel-held areas of Syria to al-Qaeda havens in western Pakistan and Yemen, and said some of the extremist groups had “aspirations” to attack the United States.

Additionally, Syria’s war — which has claimed an estimated 140,000 lives, sent millions fleeing into neighboring countries with fragile infrastructures, and left hundreds of thousands internally displaced or starving — has worsened exponentially. The crisis, U.N. Secretary General Ban Ki-moon said Thursday, has severely affected “nearly half the population of Syria.”

Finally, last month’s failed negotiations in Geneva between the opposition and Assad’s government have left the administration disillusioned about the possibility that Russia, Assad’s main backer, is prepared to play a constructive role.

Evidence of the growing breach with Russia is playing out this week at the United Nations, where a U.S.-backed Security Council resolution demands cross-border access for humanitarian aid — often denied by the Syrian government — and warns of unspecified further measures.

Russian Foreign Minister Sergei Lavrov has called the resolution, which is likely to come to a vote Friday or Saturday, a violation of international law under which only Syria can determine who legally crosses its borders. While some U.S. and other officials said they remained hopeful of agreement, others advocated pushing the measure to force a Russian veto that would embarrass Moscow during the Sochi Olympics.

U.S. and other officials said that new plans on the way to implementation call for stepped-up training of vetted opposition fighters and increased arms shipments. Most of the arms to the so-called southern front will continue to come from Saudi Arabia, which is supplying rocket launchers, some antiaircraft capability, heavy machine guns and armored vehicles in addition to small arms and ammunition.

U.S. officials said there are no plans to turn the CIA-operated training and arms assistance program over to the U.S. military.

In addition, there are still-developing plans under the new agreements to open more robust supply routes in the north, through Turkey, where so-called moderate opposition fighters are battling extremists as well as Assad’s forces. Until now, Turkey has resisted such outside operations, and some of the allies have charged the Turks with turning a blind eye to extremist infiltration. The White House said that Obama and Turkish Prime Minister Recep Tayyip Erdogan agreed in a telephone conversation Wednesday “on the importance of close cooperation between our two countries to address the growing terrorist presence in Syria.”

Not every U.S. partner is entirely pleased about what the United States is prepared to do about the recent turn of events.

“This is deja vu from two years ago,” said another Arab official, who noted that the administration’s goal remains not to promote an opposition “win” over the Syrian government, but to change Assad’s “calculus” about whether victory over the rebels is possible.

France has proposed that Obama use Assad’s foot-dragging on last year’s agreement to destroy its chemical weapons as an excuse to renew the threat of cruise missile attacks on Syrian installations. Saudi Arabia and other Persian Gulf governments have long insisted that U.S. airstrikes need no more excuse than Assad’s continuation in power.

Administration officials indicated that the United States is no closer to attacking Syria than it was two years ago, when efforts to coordinate with partner nations were first seriously initiated.

“We don’t rule those things out,” said the senior administration official, who nonetheless dismissed possible U.S. air operations in Syria as an ephemeral “silver bullet.” “Those are always options,” the official said, “but we still don’t see a cost-benefit analysis in which they change the situation on the ground sufficiently to justify the extraordinary risk” they pose.

There has been no U.S. acquiescence to a Saudi proposal to provide rebel groups with shoulder-launched ground-to-air missiles, called MANPADS, officials from several governments said.

The senior administration official discounted reports this week of major changes in the administration’s Syria policy — spurred by recent statements from Secretary of State John F. Kerry and others — as “overstated. You would think we had a formal tasking” to come up with new options, the official said. “That is not the case.”

Instead, the official cited “changes in focus, rather than changes in policy.”