WASHINGTON — The military coalition attacking the Islamic State in Iraq and Syria has been heralded by President Obama as "almost unprecedented," especially for the participation of Arab air forces. Indeed, Saudi Arabia, the United Arab Emirates, Jordan, and Bahrain have helped carry out strikes inside Syria.
But as the air operation enters its fourth month, most of the missions — including the vast majority of bombing runs — are still being conducted by US forces, with the majority of the others performed by Western allies, according to a Globe review of official statistics and interviews with officials from partner countries.
This has raised new questions about whether key Arab allies have completely bought into the US strategy, which could fail without strong — and visible — local support on the ground and in the air.
The issue is likely to play prominently when Congress reconvenes this week to debate Obama's request for $5.6 billion in war funding and a formal vote to authorize the use of force.
"This mission made sense if we are supporting regional actors willing to police extremism in their own region," said Senator Tim Kaine, a Virginia Democrat and member of the Foreign Relations Committee who recently visited the coalition's joint air operations in Qatar.
"It makes no sense if the regional actors are not willing to stand up to it and we are being called on to do what regional actors should do."
Kaine said the nature of the military coalition, including the readiness of Iraqi forces, Kurdish militias, and moderate Syrian rebels to wage an effective ground campaign, will weigh heavily on the minds of lawmakers in both parties.
"I do have some colleagues whose votes I think will depend upon the extent of the coalition," Kaine said in an interview.
The New York Times reported that the Iraqi forces' ill-preparedness to take on Islamic State in the field was also hindering the US's ability to gather intelligence for the airstrikes. And as the Iraqis try to hold back the Islamic State advance on the ground, the United States is carrying most of the load from the air, at an estimated $8 million a day.
The United States has also sent 1,500 military personnel to advise the Iraqis and secure US facilities and said Friday it will send 1,500 more to serve in a "noncombat" role in the coming months.
Statistics released by the military show the heavy reliance on US air power.
Eighty-six percent of the 8,007 missions flown between Aug. 8 and Nov. 3 were carried out by the United States, according to US Air Forces Central Command. These include bombing runs, intelligence-gathering flights, and midair re-fuelings.
The coalition expanded after Sept. 23, when the strikes were extended into Syria, to include the participation of the four Arab allies. But the United States is still flying more than 75 percent of the missions, according to the data — or 3,320 out of 4,410 since that date.
That comes even as Western allies such as Denmark, Australia, France, and Belgium have recently stepped up their role.
While the Western partners commonly discuss their role publicly, Arab governments have provided scant information since the widely publicized strikes in September.
One exception is Bahrain, which participated in the initial phase of airstrikes against ISIS in Syria in late September but has not dropped bombs since September, according to Salman Al Jalahma, a spokesman for Bahrain's embassy in Washington.
"The airstrikes have been the extent of our military participation," he said.
Other Arab participants in the military coalition declined to provide details, including Qatar, the United Arab Emirates, and Jordan. The government of Saudi Arabia did not respond to multiple requests for comment.
Even many of the attack missions attributed to Arab nations are limited in nature, according to US military officials.
For example, while the Gulf nations have participated in more than 20 percent of the fighter sorties in Syria, their pilots are often serving as "mission commanders" or "escorts."
Mission commanders don't always drop bombs and escorts generally never do, according to the command.
A US military spokesman, however, defended the Arab role in the military coalition.
"Their contributions to air operations have been significant," said Air Force Lieutenant Colonel Edward Sholtis.
He said military officers from Gulf nations are also serving as liaison officers inside the so-called Coalition Air Operations Center in Qatar.
The total number of nations contributing financially or in the form of humanitarian aid to Operation Inherent Resolve is much larger than those engaged in military operations — some 60 nations, the US State Department said.
But the military coalition, particularly the Arab role, has been seen as critical.
"Their contributions will not be on the level of NATO allies, let alone US forces, but they can be helpful," said Christopher S. Chivvis, a military specialist at the government-funded Rand Corp.
"In the 2011 Libya intervention, the participation of Qatar, UAE, and Jordan was viewed by US policy makers as a broader demonstration of Arab support."
Yet the relatively modest contributions of the Arab partners, which all operate US-manufactured fighter jets outfitted with precision guided bombs, are viewed by some specialists as reflecting Arab leaders' concerns about becoming too embroiled in the fight against the Sunni militant group that has adherents in some of their own countries.
"At the end of the day everybody wanted the United States to come and use the Air Force so everyone could have an alibi," Soli Ozel, a professor of international relations and political science at Istanbul Bilgi University in Turkey, said at a conference convened late last month by the Carnegie Endowment for International Peace in Washington.
Others expressed concern the conflict is being perceived by many people in the region — especially the young and unemployed who are considered potential recruits for the Islamic State — as another example of US military interventionism.
"You talk to them and they clearly tell you 'this is not our war,'" said Marwan Muasher, vice president for studies at the Carnegie Endowment.
"They don't see it as a cultural war; they don't see it as a war for values. They see it as an American war against the region. And if it is an American war against the region, they are not going to side with the Americans."
Bill Roggio, a senior fellow at the Foundation for Defense of Democracies, a hawkish Washington think tank, said a major problem now is that when it comes to the United States' regional allies, "you have a coalition of partners that all have different agendas."
"They are in it now, but how long are they in it?" he asked.