Last week, U.S. officials said there was evidence that Syrian forces had begun preparing sarin, a nerve agent, for possible use in bombs.
Speaking to reporters flying with him from Washington to Kuwait, Panetta suggested the threat was no longer escalating, although he was not specific about any Syrian military preparations.
"At this point the intelligence has really kind of leveled off," he said. "We haven’t seen anything new indicating any aggressive steps to move forward in that way."
Panetta was in Kuwait to visit U.S. troops at the start of a four-day trip. The U.S. has about 13,500 troops in this country; they are a remnant of the 1991 Gulf War in which a U.S.-led coalition force evicted Saddam Hussein’s Iraqi army after it invaded Kuwait in August 1990.
Asked whether he believed Syrian President Bashar Assad was heeding Western warnings against using chemical weapons, Panetta said: "I like to believe he’s got the message. We’ve made it pretty clear. Others have as well."
He noted that the Assad regime is coming under increasing pressure from rebel forces.
"Our concern is that if they feel like the regime is threatened with collapse, they might resort to these kinds of weapons," he said.
Syria is believed to have a formidable arsenal of chemical weapons, including sarin and mustard gas, although its exact dimensions are not known. Syria is not a signatory to the 1997 Convention on Chemical Weapons and thus is not obliged to permit international inspection.
In the interview with reporters on his flight from Washington, Panetta also said he expects Obama administration decisions in the next few weeks on what military missions and forces the U.S. will seek to keep in Afghanistan after its combat mission ends Dec. 31, 2014.
The U.S. now has about 66,000 troops in Afghanistan as part of an international coalition that has been fighting the Taliban for more than 11 years.
Panetta said he would consult further with Marine Gen. John Allen, the top coalition commander in Kabul, before making further recommendations to President Barack Obama on a post-2014 military presence.
Panetta also said he is encouraged by what he called a downward trend in the number of attacks on U.S. and coalition forces by their Afghan partners. These so-called insider attacks accelerated for much of 2012, threatening to disrupt the U.S.-Afghan military partnership.
Panetta said the number of such attacks fell from 12 in August to two in November.
"Steps that were put in place to try to deal with that threat I believe have been effective," he said. He did not mention specific steps, but they include more rigorous vetting of Afghan army and police recruits and a requirement that U.S. troops carry loaded weapons at all times, even when on coalition or Afghan bases.