The Obama administration Tuesday appeared to temper its recent assertions that the Syrian government may be preparing to use chemical weapons, with Secretary of Defense Leon Panetta telling reporters the relevant intelligence had "really kind of leveled off."

"We haven't seen anything new indicating any aggressive steps to move forward in that way," Panetta told reporters during a flight to Kuwait, adding that U.S. officials "continue to monitor it very closely and we continue to make clear to them that they should not under any means make use of these chemical weapons against their own population. That would produce serious consequences."

U.S. officials told CBS News correspondent David Martin just last week that monitoring of roughly two dozen bases where President Bashar Assad is believed to have chemical weapons stored indicated the regime had begun preparing the materials, including sarin gas, for use. Satellites had seen trucks moving among the bunkers where the weapons and agents are believed to be stored. U.S. officials told Martin the evidence was strong, but circumstantial -- not definitive.

Rebel fighters have now inched so close to Assad's stronghold, the capital city of Damascus, that top U.S. officials had expressed fears the cornered dictator could try and use his chemical weapons as a last resort to try and avoid being toppled by the 21-month uprising.

Syrian government officials have refused to confirm that they even posses chemical or biological weapons -- saying only that if they did have them, they would not use them against the Syrian people, or anyone else.

Panetta himself never said publicly that Assad was preparing chemical weapons. He, along with Secretary of State Hillary Clinton, instead issued repeated, terse warnings to Assad not to take the step.

"There is no question that we remain very concerned, very concerned, that as the opposition advances, in particular on Damascus, that the regime might very well consider the use of chemical weapons," Panetta said last week.

Asked Tuesday whether the drop in alleged evidence pointing to chemical weapons preparations might indicate that Assad had heeded the warning, Panetta said: "I'd like to believe he's got the message, we've made it pretty clear and others have as well. But you know it's also clear that the opposition continues to make gains in Syria and our concern is that if they feel like the regime is threatened with collapse that they might resort to these kinds of weapons."

A senior member of Assad's regime who defected recently tells CBS News, however, that the dire warnings of a possible sarin gas attack by Assad's military seem overblown. The defector, who maintains contact with Syrian military commanders, says those commanders deny any recent movements of chemical weapons components.

The commanders also have told the defector that logistically, they cannot see how the regime would try and use the deadly weapons effectively against the rebels -- which the regime regularly refers to as "terrorists" -- they are such a small and mobile enemy.