The vote passed by a large majority in the Republican-controlled House and is expected to be adopted in the Senate.
The endorsement came after President Barack Obama repeated that he would not be committing American combat troops to ground operations in Iraq.
The US has undertaken 174 air strikes against ISIS in Iraq since mid-August.
The jihadist group controls large areas of Syria and northern Iraq.
In the most recent air strikes on September 16 and 17, US forces destroyed two ISIS armed vehicles north-west of Irbil and several units south-west of Baghdad, according to US Central Command (CENTCOM).
Barack Obama’s new strategy plans similar attacks in Syria and calls on a coalition of 40 countries to confront the militant group.
This vote was expected to pass easily. Republicans, who control the House, generally support Barack Obama’s strategy to defeat and degrade Islamic State.
But the more hawkish among them feel the plan falls short. They argue that the president should consider sending US combat troops to Syria and Iraq – something he has said he is not prepared to do.
Some lawmakers from both parties feel skeptical that the Syrian rebels are up to the job.
At a Senate committee hearing, they pressed Secretary of State John Kerry for assurances that the Syrian fighters would be properly vetted so that, in future, American weapons don’t fall into the wrong hands.
On September 17, the House of Representatives approved his $500 million request by 273 votes to 156 to help arm and train moderate rebels in Syria.
The provision has been added to spending legislation aimed at extending federal government operations beyond the end of September.
Earlier, Barack Obama said he would not commit “to fighting another ground war in Iraq”, while visiting a military base in Florida.
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