A senior White House official says it would be difficult and costly to set up a no-fly zone over Syria and the United States does not have a national interest in pursuing that option.
After months of deliberation, Mr Obama's administration has announced it would supply arms to the rebels, having obtained proof the Syrian government used chemical weapons against fighters trying to overthrow President Bashar al-Assad.
The US has given no details about the military aid, other than that it would be different in scope and scale to what it had provided before, which had been limited to providing rations and medical supplies to rebel forces.
The commander of Syria's main rebel fighting force urged Western allies to create a no-fly zone
However, US deputy national security advisor Ben Rhodes said the US did not want to send troops to Syria, and enforcing a no-fly zone over the country would carry with it great and open-ended costs, Reuters reports.
"We have to make these decisions based on US national interest, and we don't at this point think believe that the US has a national interest in pursuing a very intense, open-ended military engagement through a no-fly zone at this juncture.
"It's far more complex to undertake the type of effort, for instance, in Syria than it was in Libya."
Syria denies chemical weapons use
The Syrian government dencounced the claims over chemical weapons as lies and accused Washington of using fabricated information.
Syria's foreign ministry said the US was resorting to "cheap tactics" to justify President Barack Obama's decision to arm the rebels.
Russia says evidence of chemical weapons use presented by the US did not look convincing, while UN leader Ban Ki-moon said arming either side in the Syria conflict would not be helpful.
A rebel leader Salim Idris told the BBC new weapons would help the rebels defeat the Assad regime and defend civilians.
General Idris, leader of the Supreme Military Council (SMC), said the US administration's decision was a "very important step"
"We are in most need for anti-tank missiles and anti-aircraft missiles and in addition to all of that we need a huge amount of weapons and ammunition to stop the offensive of the regime," he added.
The CIA is expected to co-ordinate delivery of the military equipment and train the rebel soldiers in how to use it, US media reports said.
The UN says two years of conflict has killed at least 93,000 people, and more than 1,700 children under the age of 10 have died.