US legislators have voted to authorise training and arming of vetted Syrian rebels to combat fighters of the Islamic State of Iraq and the Levant (ISIL), which controls large parts of Iraq and Syria.

The House of Representatives on Wednesday voted 273 to 156 to approve President Barack Obama's train-and-equip plan despite misgivings by both Democrats and Republicans.

Some Democrats said the move could open the door to full-blown American military intervention in the Middle East. Conservative members are concerned that the plan falls short of what is needed to defeat the ISIL.

The measure is attached to a stopgap spending bill also expected to pass the House on Wednesday.

The legislation must be passed by the Senate before it can be sent to Obama to sign into law.

Obama has pressed Congress to provide him political cover to initiate military action in Syria against ISIL, although the White House and many politicians believe he has the constitutional authority to launch air strikes in

Syria, as he has done in Iraq, to protect US national security interests.

House Speaker John Boehner hailed the vote as "an important, initial step forward in taking on the Islamic State of Iraq and the Levant".

The measure was crafted by Buck McKeon, House Armed Services Committee chairman, who was among many Republicans who feel Obama's plan does not do enough to meet the goal.

With Democrats largely split on the issue, the party's House number two Steny Hoyer took to the floor to rally Congress to back the commander-in-chief in a time of crisis.

"We are united in our resolve to meet this threat. We clearly may have differences on this House floor, but we are Americans when it comes to defending our people, and our country," Hoyer said.

"We know empirically the cost of doing nothing is far too great."

With the amendment attached to the temporary spending bill that expires on December 11, legislators are gearing up for a broader debate - after congressional midterm elections on November 4 - on whether to approve a new authorisation for the use of military force to give Obama powers to prosecute a wider war against the fighters in Iraq and Syria.

McKeon's amendment puts important checks on Obama's power, including a prohibition against sending US combat troops to Syria and requirements that the administration keep Congress in the loop with regular reporting about the mission.

Speaking to Al Jazeera, William Fallon, former admiral and commander of the US Central Command, said Obama needs more allies to join air raids for his ISIL strategy to work,

"The Obama administration is going to great lengths - there are 40 other countries taking part in the effort," he said.

"But only two other countries have planes in the sky over Iraq. A lot of critics say, for this strategy to work Arab nations have to contribute to the military effort."