WASHINGTON — The Republican-controlled House today approved a $585 billion defense policy bill that grants President Barack Obama the authority to expand the U.S. military campaign against Islamic militants in Iraq and Syria.

The vote was 300-119, a reflection of the popularity of the sweeping, bipartisan measure that authorizes funds for American troops as well as ships, planes and other war-fighting equipment built in congressional districts nationwide.

The measure heads to the Senate where passage is expected next week.

The legislation endorses Obama’s latest request to Congress in the 4-month-old war against extremists who brutally rule large sections of Iraq and Syria. The bill provides $5 billion for the stepped-up operation of air strikes and the dispatch of up to 1,500 more American troops.

It also reauthorizes the Pentagon plan to train and equip moderate Syrian rebels battling the forces of President Bashar Assad, with that mandate expiring Dec. 11. The legislation would extend that authority for two years.

Still, war-weary lawmakers expressed considerable unease about a slippery slope for the American military after years of conflicts in Afghanistan and Iraq.

“We’re getting more deeply involved in the war in Iraq and Syria,” complained Rep. Jim McGovern, D-Mass.

The top Democrat on the House Armed Services Committee, Rep. Adam Smith of Washington, insisted that U.S. involvement was limited.

Smith said. “I don’t want U.S. combat troops fighting this ground war .... By training and equipping the Syrians and Iraqis, we can empower them to fight their own ground war with our support from the air.”