Decisions by France and Britain to step up direct support for Syrian opposition forces, possibly with arms shipments to the rebels, threaten to leave the United States on the sidelines of what many see as the approaching climax of a two-year-old effort to oust President Bashar al-Assad.

That may be precisely where the Obama administration decides to stay, once it concludes a renewed internal debate over whether to pursue a more aggressive policy in Syria.

But U.S. hesi­ta­tion has frustrated some of Washington’s closest European and Middle Eastern friends, who say that the time for debate is fast running out. More than 70,000 Syrians have been killed and millions have fled their homes. The raging conflict has begun to spill over Syria’s borders, and no negotiated end is in sight. ­

“We’re at the point where we have to show some real progress,” said a senior official from a Middle Eastern government that actively supports the Syrian rebels. Sophisticated weapons that could help break a months-long military stalemate in and around Damascus and consolidate rebel gains in other parts of the country, he said, could finally persuade regime supporters to break with Assad and hasten his downfall.

Beginning last fall, “everyone was waiting for a new administration, then a new cabinet” in Washington to formulate and lead a new joint strategy, the official said. If Assad and his military now “see business as usual, then he could survive,” the official said.

A look at the Syrian uprising nearly two years later. Thousands of Syrians have died and President Bashar al-Assad remains in power, despite numerous calls by the international community for him to step down.

Anti-Assad governments in the region, including Saudi Arabia, Turkey and Qatar, are privately acerbic in their assessment of U.S. dithering. The Europeans express more understanding, even as they question whether the Obama doctrine of close coordination on issues of shared foreign policy concern is viable if the United States declines to participate.

“It slightly undermines the model” established with the military intervention in Libya, a senior European official said. There, President Obama took credit for organizing and supporting a strategy implemented along with European and Persian Gulf partners.

“We would hope the Americans would join us” on Syria, the official said.

Officials from several European and Middle Eastern governments agreed to discuss Syria policy only if they were not identified by name or country to avoid antagonizing the United States.

Last week, Britain and France broke away from what had been a cautious united front with the Obama administration on Syria.

At a European Union meeting in Brussels on Friday, France called for an end to an E.U. arms embargo that has prevented weapons shipments to the Syrian rebels and indicated it was prepared to act on its own if others disagreed. The rebel coalition “needs to have the means to defend the areas that have been liberated,” French President Francois Hollande said.

British Prime Minister David Cameron backed the call to end the embargo and appeared to directly address U.S. concerns in a Brussels news conference.

“I think it’s worth taking on for a moment the two arguments that the opponents of change make. The first is that what is required in Syria is a political solution, not a military solution. Well, of course people want a political solution . . . but this is not an either-or situation,” Cameron said, adding that political progress was more likely if democratic opposition forces were seen as growing stronger.

The second argument, he said, was that “the arms will go to the wrong people, to which my answer is: That is what has happened already,” as Islamist radicals in the rebel ranks have strengthened their arsenals.

Last fall, the White House rejected proposals to arm the rebels, supported by then-leaders of the State Department, the Pentagon and the CIA. In addition to fears that sophisticated weapons would end up with extremists, it concluded that opposition political unity was a higher priority.

It remains unclear where the new national security leadership stands under Secretary of State John F. Kerry, Defense Secretary Chuck Hagel and CIA Director John O. Brennan. Beyond the administration’s intense focus on domestic issues, the White House has been distracted by Obama’s upcoming trip to Israel. Syria is only one of several foreign policy crises, including North Korea and Iran, competing for urgent attention.

There has been some incremental movement over the past several weeks, based on decisions that a senior administration official said have come “directly from the president” in response to growing “dangers on the ground” in Syria and a recognition of opposition progress.

Traveling overseas for meetings with allies and Syrian rebel political leaders, Kerry publicly acknowledged for the first time that the United States was coordinating with governments already sending arms and has confidence that “the weapons are being transferred to moderates.” A small contingent of U.S. forces, working with the Jordanian military, is reportedly training some rebel forces at a camp north of Amman.

Kerry announced that the United States would provide humanitarian aid directly to the Syrian opposition’s political coalition and would provide food and medical supplies to the rebel military. He told allied governments that he would bring their pleas for more U.S. involvement back to Obama.

But the administration is not alone in its reluctance to send arms. At Friday’s meeting of the 25-member E.U., Germany, the Scandinavian countries and others disagreed with French and British insistence that the embargo be dropped.

“Just the fact that two have changed their minds doesn’t mean that the other 25 have to follow suit,” German Chancellor Angela Merkel said.

The issue will be debated again in coming days, when E.U. foreign ministers meet in Dublin. The existing embargo lapses at the end of May. If it is not renewed by unanimous vote, each country will be free to act as it wishes. Britain and France would like a new version that continues sanctions on Assad’s government while allowing arms shipments to the rebels.

There are similar splits in opinion in this country. A number of Republican leaders have accused the administration of inaction, some Democrats have warned against a new foreign involvement, and the public is weary of faraway wars.

Even Britain and France — and the United States, should it eventually decide to join them — are unlikely to provide everything the rebels and their supporters in the region say they need. Air support remains highly unlikely, absent Assad’s use of chemical weapons, as do portable surface-to-air missiles, which the rebels want to shoot down Assad’s helicopters and jets.

But as the United States’ closest allies in Europe move rapidly toward a new level of involvement, Cameron said, the important thing is “persuading people who have been less willing to move on this that there really [are] very strong arguments for saying that what is happening now isn’t working.”