WASHINGTON—The Obama administration is considering scrapping its effort to create a large-scale Syrian force to fight Islamic State as it searches for alternatives to prevent the American-led effort from collapsing, officials said.

Under one proposal being crafted at the Pentagon, the $500 million train-and-equip program—a core component of the U.S. Syria strategy—would be supplanted by a more modest effort focused on creating specially trained militants empowered to call in U.S. airstrikes, defense officials said.

The reconsideration comes after new disclosures of failures in the U.S. strategy in Syria, which is under intensified scrutiny at home and abroad. The overhaul in the training mission is one of a number of important changes in the Syria policy under discussion, the officials said.

The White House is also debating whether to accept a Russian proposal for talks on military activity in Syria as Moscow builds up military support for President Bashar al-Assad’s embattled regime. At the same time, the White House wants to reignite long-stalled international talks aimed at reaching a resolution to Syria’s multi-sided war.

“They look at this thing and they’re frustrated too,” one senior defense official said of Pentagon leaders.