Gen. Lloyd Austin III, commander of the U.S. Central Command, told Congress on Wednesday that only “four or five” trainees from a U.S. program have actually ended up “in the fight” against the Islamic State in Syria. (Chip Somodevilla/Getty Images)

The Obama administration is moving toward major changes in its military train-and-equip program for the Syrian opposition after the acknowledged failure of efforts to create a new force of rebel fighters to combat the Islamic State there.

In comments that appeared to shock even many of those involved in Syria policy elsewhere in the government, Gen. Lloyd J. Austin III, the head of the U.S. Central Command, told Congress on Wednesday that only “four or five” trainees from the program, a $500 million plan officially launched in December to prepare as many as 5,400 fighters this year, have ended up “in the fight” inside Syria.

The course correction would mark the first significant alteration in the Obama administration’s year-old strategy of defeating the militants with air power, along with training and supplies for indigenous forces fighting them on the ground. It comes as critics have drawn a direct line between Obama’s long-standing reluctance to more directly intervene in the fight and the growing flood of Syrian refugees fleeing to the West.

Defense officials who described the proposed changes said the yearly goal would be substantially lower, perhaps as few as 500. Rather than front-line forces, fighters would be trained as enablers and liaisons between U.S. forces outside the country — particularly those directing U.S. airstrikes — and groups such as Syrian Kurds and Sunni Arabs that the Pentagon thinks have been effective against the militants.

Vetting rules would be eased to allow training for members of groups previously barred from training, according to officials who spoke on the condition of anonymity because they were not authorized to describe the changes. Obama’s senior national security officials discussed the Syria situation in a principals meeting at the White House early this week.

Lawmakers responded to Austin’s description of overall progress against the Islamic State in Syria and Iraq with near-universal skepticism, and they described the administration’s strategy of defeating the militants with air power, along with training and supplies for indigenous forces on the ground, as a failure. Sens. Timothy M. Kaine (D-Va.) and Angus King (I-Maine) declared themselves converts to the need to establish a U.S.-protected safe zone for refugees and opposition fighters inside Syria, a proposal the administration has repeatedly rejected.

“I hate it when the chairman’s right, but he’s been talking about this for two years, and I — in retrospect, I think he was right,” King said of Senate Armed Services Committee Chairman John McCain (R-Ariz.), who has long pushed for direct U.S. intervention in Syria against the forces of President Bashar al-Assad as well as the Islamic State.

“We’ve allowed this atrocity to go on too long, and it’s impacting us; it’s impacting the rest of Europe,” King said of the tens of thousands of Syrian and other Middle East refugees pouring into Europe. “I really thing there should be a rethinking of the non-intervention strategy.”

McCain called the administration’s strategy an “abject failure” and said “the refugees are a result of it.” Under withering questioning from McCain, Austin repeated that he would not recommend establishing such a zone “at this time.”

After a summer of focusing on the Iran nuclear deal and the 2016 presidential race, Congress has again turned its attention to the wars in Syria and Iraq, and lawmakers made clear they do not like what they see. In addition to the sudden flood of refugees — fleeing Syria as well as camps and cities in Turkey and Jordan, where millions have been largely out of sight to the rest of the world — concern has escalated with this month’s Russian military buildup near the Syrian port of Latakia.

Both of those situations have created new headaches for an administration already flailing in the region. While the administration has said that Assad must step down, it has declined to throw its military weight behind forces seeking to oust him. Instead, U.S. air strikes and most assistance have been restricted to the separate but overlapping fight against the Islamic State in Syria and Iraq.

Russia, Assad’s principal diplomatic and military backer — along with Iran — has said its new Syrian deployments are designed to assist the fight against the Islamic State, not to further aid Assad.

“Obviously, there are serious questions. . . . I’m not taking that at face value,” Secretary of State John F. Kerry said Wednesday. “We look at the type of airplanes or the type of munitions and so forth, and it obviously raises much more serious questions about what is happening.”

So far, Russia has begun work on expanding airstrips and has transferred tanks and armored personnel carriers to the Syrian coast.

Kerry has carried the ball for the administration in complaining to Russia, speaking three times by phone with Foreign Minister Sergei Lavrov in less than a week.

This week, he said, the Russians suggested that the conversation be expanded to a “military-to-military” dialogue “in order to discuss the issue of precisely what will be done to de-conflict,” and avoid the eventual possibility that Russian aircraft and those belonging to the U.S.-led coalition bombing the Islamic State in Syria encounter one another.

Kerry said he still thought that “meaningful” Russian help could contribute to a political solution in Syria.

Administration officials said that dialogue would likely begin with a phone call between Russian Defense Minister Sergei Shoigu and Defense Secretary Ashton B. Carter, who has so far shunned such contact. As recently as late Tuesday, Pentagon press secretary Peter Cook said that because Kerry was in touch with Lavrov, “to date there has been no reason for Secretary Carter to initiate another” line of communication.

The administration shut down military-to-military engagements with Russia in March 2014 because of Russia’s “aggressive actions in Ukraine,” Cook said, although “senior leaders continue to have the discretion to communicate with their counterparts as necessary.”

Kerry, officials said, sees the opening of a military dialogue as a way to determine Russian intentions and avoid escalating what could become a dangerous situation.

In his testimony, Austin acknowledged that progress in Syria and Iraq was slow, but he gently disputed the term “stalemate,” recently used in testimony by Gen. Martin E. Dempsey, the outgoing chairman of the Joint Chiefs of Staff. Austin said he spoke with Dempsey this week about the word, and Austin noted that Dempsey had also testified that “ISIL’s future is increasingly dim.” ISIL is an acronym for the Islamic State.

But, he said, “I agree with the chairman. . . . There haven’t been any dramatic gains on either side.”

Missy Ryan, Carol Morello and Thomas Gibbons-Neff contributed to this report.