WASHINGTON - The Obama administration is overhauling its approach to fighting the Islamic State in Syria, abandoning a failed Pentagon effort to build a new ground force of moderate rebels and instead partnering with established rebel groups, officials said Friday.

The shift, telegraphed weeks ago by disclosures that the effort had produced only a handful of trained rebels, is meant partly to take better advantage of U.S. airpower, which can play a bigger role now that Turkey is permitting American fighter jets to operate from its soil. But it is not expected to immediately give new momentum to a slow-moving -- some would say stalled -- American-led campaign against the Islamic State.

The aim is to work with established rebel units "so that over time they can make a concerted push into territory still controlled by ISIL," said Pentagon press secretary Peter Cook. Others said the hope is to put much more pressure on the northern city of Raqqa, the Islamic State's declared capital.

The change also reflects growing concern in the Obama administration that Russia's intervention has complicated the Syrian battlefield and given new life to President Bashar Assad. Russian airstrikes have raised questions about whether and how the U.S. would protect rebel groups it is working with if they are hit by Russian bombs.

Meanwhile, the CIA has since 2013 trained some 10,000 rebels to fight Assad's forces. Those groups have made significant progress against strongholds of the Alawites, Assad's sect, but are now under Russian bombardment. The covert CIA program is the only way the U.S. is taking on Assad militarily.

The administration is under heavy criticism in Congress for a flawed approach in Syria, amplified by Russia's muscular moves to launch ship-based cruise missile strikes and deploy fighter aircraft and battlefield weaponry -- actions that caught the U.S. by surprise and underscored the failure of the Pentagon's $500 million program to train and equip rebels.