WASHINGTON — President Barack Obama’s strategy to combat Islamic State extremists in Iraq and Syria is being scrutinized in Congress, where the expanded military campaign has broad support but faces skepticism rooted in more than a decade of war.

Defense Secretary Chuck Hagel and Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, were scheduled to testify today before the Senate Armed Services Committee, the first in a series of high-profile Capitol Hill hearings that will measure the president’s ability to rally congressional support.

Obama last week outlined his military plan to destroy the extremists, authorizing U.S. airstrikes inside Syria, stepping up attacks in Iraq and deploying additional American troops, with more than 1,000 now advising and assisting Iraqi security forces to counter the terrorism threat. The U.S. conducted the first of the airstrikes Monday, going to the aid of Iraqi security forces who were being attacked by enemy fighters.

The president said he had the authority to order the airstrikes without new congressional approval. Obama did ask Congress to authorize a program to train and arm vetted Syrian rebels battling the Islamic State group and forces loyal to Syrian President Bashar Assad, a program that got a boost Monday as House Republicans pushed to authorize the mission.