The odor of smelly feet may one day soon be a thing of the past at airport security checkpoints. (ERIK S. LESSER/ASSOCIATED PRESS)

“You’re going to see better technology over time” that will make it easier to keep your shoes on, but Napolitano would not specify exactly when the changes would occur or what technology is making the process easier.

“In terms of what we see coming in the months and years ahead, it will probably be easier, and it looks like it will be, to deal with the shoe issue before we can lift restrictions on liquids,” she said.

Transportation Security Administration officials and other aviation security experts caution that the general public is unlikely to enjoy such changes for some time. Frequent fliers enrolled in a TSA-backed program would likely be the first to enjoy a new no-shoes-off rule, they said.

Napolitano said restrictions on liquids are likely to continue in part because intelligence reports suggest that terrorists are still attempting to use non-metallic detonation devices aboard commercial airliners operating in the United States and Europe.

“Terrorists abroad continue to focus on aviation,” she said. “Why? Because aviation [attacks] succeeded in the past.”

Napolitano spoke Tuesday morning at a breakfast hosted by Politico. She is making a series of appearances this week in Washington, New York and Boston to mark the 10th anniversary of the Sept. 11 terrorist attacks.

Millions of air passengers in the U.S. take their shoes off at airport security lines every week because of one act: Three months after the 2001 attacks, British-born Richard Reid tried to set off a bomb in his shoe on an American Airlines flight from Paris to Miami. A self-proclaimed al-Qaeda member, he was subdued by the crew and passengers.

There hasn’t been another shoe bomb attempt since, and aviation security experts question whether shoe removal is necessary.

“You don’t take your shoes off anywhere but in the U.S. — not in Israel, in Amsterdam, in London,” said Yossi Sheffi, an Israeli-born expert on risk analysis at Massachusetts Institute of Technology. “We all know why we do it here, but this seems to be a make-everybody-feel-good thing rather than a necessity”

John S. Pistole, the TSA administrator, cites a travel industry survey that found shoe removal was second only to the high price of tickets in passenger complaints. But he is unapologetic about the practice.

“We have had over 5.5 [billion] people travel since Richard Reid and there have been no shoe bombs because we have people take their shoes off,” Pistole said last month.

But he recognizes the “hassle factor” and hopes that passengers who sign up for an upcoming trusted traveller program will be exempted from some current security measures, including shoe removal. At some point, when technology is developed to ensure that everyone’s shoes are bomb-free, TSA expects to drop the shoe removal requirement.

Overall, however, Pistole has been moving the TSA toward a system that relies more on intelligence and passenger observation than technology.

It is an approach that is endorsed by independent experts on airline security.

“Richard Reid left a trail of suspicion with everybody who was in contact with him during the boarding process, yet Richard Reid was allowed to board an American Airline flight,” said Rafi Ron, former director of security at Ben Gurion International Airport in Tel Aviv and now a security consultant in the U.S. “Both Richard Reid and [Umar Farouk] Abdulmutallab [the underwear bomber] checked into a transatlantic flight without checking any baggage, which is very unusual. Both had one-way tickets. There were a lot more red flags about them, but I’m not sure we should go into all the details in the public media. If we used these in an effective manner, they would have been identified.”

Vahid Motevalli, head of the department of mechanical engineering technology at Purdue University, said that even though Reid’s attempt failed, it succeeded in adding a costly and frustrating layer of security.

“As a result of Reid, now everybody has to take their shoes off and we’ve added another expense,” Motevalli said. “These events create fears, disrupt lives and change the way you’re living. By that standard, that attempt was successful.”

Follow Ed O’Keefe on Twitter: @edatpost