The CIA has already begun shipping weapons to a secret network of warehouses in neighboring Jordan, in an operation backed by European and Arab powers. It will provide training to forces that are supposedly "moderate" and "separate" from Al Qaeda-linked forces such as the Al Nusra Front.
The shipments will fuel an August offensive against the regime of Bashar al-Assad.
The Obama administration cited unsubstantiated US and French claims that pro-Assad forces have used chemical weapons such as sarin on 10 separate occasions to claim that a "red line" has been crossed justifying an open policy of arming the opposition.
Vast quantities of weaponry have already been sent via Saudi Arabia to Islamist groups. Washington now claims that weapons sent to "moderates" are the best means of ensuring that Al Nusra's dominant role can be challenged. This is supposed to be guaranteed by CIA oversight and training by US special operations forces. But the CIA will spend a mere two weeks vetting and training an initial group of fighters.
The US already has 1,000 troops in Jordan providing training.
France is considering sending arms "to balance" the military aid received by the Assad regime from Russia, Iran and Hezbollah, according to Foreign Minister Laurent Fabius.
In Britain, there is substantial domestic political opposition to sending arms, including within the ruling Conservative Party and its Liberal Democrat coalition partners. This has forced Prime Minister David Cameron to promise a vote in parliament on the issue that might make him dependent upon the opposition Labour Party.
Labour Leader Ed Miliband was invited Wednesday to discuss Syria at the National Security Council in 10 Downing Street. He was last invited to attend a National Security Council meeting in 2011, to sign off on the government's decision to take military action against former Libyan leader Colonel Muammar Gaddafi.
Cameron has also said the government reserves the right to act in the national interest without parliamentary assent.
Washington's reliance on Saudi Arabia to arm the opposition gives the lie to all claims that it is seeking to prevent Al Qaeda securing weapons, given Saudi intelligence agencies' close ties to far-right Islamist forces throughout the region.
On Tuesday, speaking alongside US Secretary of State John Kerry, Saudi Foreign Minister Prince Saud al-Faisal said that Saudi Arabia would help the Syrian opposition fight in an "invaded country" that was facing "genocide" in "the most effective way we can."
Saudi Arabia and Qatar will provide heavy weaponry, including hand-held surface-to-air missiles.
Kerry said, "We share a belief with Saudi Arabia and many countries that ... this next period of time is an important period of time where decisions could be made that could affect the region for years to come."
His only caveat on supplying weapons was that "we want to make sure that's being done in a coordinated way."