Many critics of the new rules contend that in addition to adding an unnecessary threat to the safety of airline crews and passengers, the changes won't make a difference in the TSA's ability to concentrate on other threats.

Knives are probably the most common items surrendered by passengers at screening points, aside from liquids.

Travelers surrender about 35 knives at Baltimore-Washington International Airport on an average day and about 47 per day at Los Angeles International Airport, officials say.

"Today, we find on average of four guns at checkpoints, but we also find about 2,000 of these small pocket knives every day," Pistole said on Thursday.

"On average that takes two to three minutes for the pocket knife to be identified, for that bag to be pulled, for that bag to be opened, for the knife to be found," he added.

That's valuable time, he said, noting that other more dangerous items could slip by security screeners.

Questioned by reporters, White House spokesman Jay Carney said he did not think President Barack Obama had a response to the issue.

"I'm sure that the TSA has been asked this question and explained their thinking in making decisions like this; DHS as well, I assume," Carney said of the TSA's parent agency, the Homeland Security Department.

"My understanding as a layman, as an observer, not as somebody who has worked the policy process, is that this has to do with an assessment of where the most likely threats are," Carney said.