Ahead of the crucial vote Barack Obama said that the US has a broad plan to help rebels defeat President Bashar al-Assad's forces but remained adamant that there would be no American boots on the ground.
ITV News Washington Correspondent Robert Moore reports:
After a meeting with congressional leaders at the White House Obama called for a prompt vote as many of those leaving the meeting put their support behind the president, including Republican leaders.
As lawmakers prepare to debate any action Secretary of State John Kerry and Secretary of Defence Chuck Hagel faced questions from a senate committee hearing.
Mr Kerry told the senators that it was beyond a reasonable doubt that chemical weapons had been deployed by the Assad regime.
However as the rhetoric in America gathered pace ahead of the key vote UN Director General Ban Ki-moon warned that any action without a mandate from the United Nations could be illegal.
He also cautioned that any US interference could "unleash more turmoil" in the region.
France is also preparing to vote on possible military action. President Francois Hollande said he would not take any action without the US.
Ahead of that vote the Syrian Government wrote a letter to French parliamentarians that they could work together to find a diplomatic solution.