WASHINGTON (Reuters) - Senator John McCain said on Monday that a vote by the Congress against President Barack Obama's proposal for using military force in Syria would be catastrophic.

"If the Congress were to reject a resolution like this after the president of the United States has already committed to action, the consequences would be catastrophic," McCain told reporters after a meeting with the president at the White House. McCain, a Republican, said he was encouraged by the meeting but that there was "a long way to go" to get the resolution passed.

McCain said that he and Republican Senator Lindsey Graham - who was also in the meeting with Obama - favored changes in the resolution that would broaden it to make it more than just a response to the use of chemical weapons by the government of Syrian President Bashar al-Assad.

"We do want an articulation of a goal that over time will degrade Bashar al-Assad's capabilities, increase and upgrade the capabilities of the Free Syrian Army and the Free Syrian Government so they can increase the momentum on the battlefield," McCain said.

Both McCain and Graham have long favored U.S. intervention against Assad in the civil war in Syria, while Democrat Obama has tried to stay out of the conflict until now.

"We appreciate the president meeting with us. We had a candid exchange of views and I think we have found some areas that we can work together. But we have a long way to go," McCain said.

(Reporting by Susan Cornwell and Deborah Charles; Editing by Eric Beech)