Nearly two-thirds of Americans support the new full-body security-screening machines at the country's airports, as most say they put higher priority on combating terrorism than protecting personal privacy, according to a new Washington Post-ABC News poll.

But half of all those polled say enhanced pat-down searches go too far.

The uproar over the new generation of security technology, and the frisking of those who refuse it, continued Monday with Homeland Security Secretary Janet Napolitano saying the new measures are necessary for public safety.

"There is a continued threat against aviation involving those who seek to smuggle powders and gels that can be used as explosives on airplanes," she said. "The new technology is designed to help us identify those individuals."

According to the Transportation Security Administration, less than 3 percent of travelers receive the pat-downs.

But Napolitano said the TSA would "listen to concerns. Of course we will make adjustments or changes when called upon, but not changes or adjustments that will affect the basic operational capability that we need to have to make sure that air travel remains safe."

One possibility that could generate public support is the use of profiling at airports, where the TSA would single out specific passengers for extra screening based on available information. Overall, 70 percent of Americans back the idea, which has been floated as an alternative.

White House spokesman Robert Gibbs sought to reassure the traveling public that "the evolution of the security will be done with the input of those who go through the security." But he said that safe travel remains the higher priority.

Some people upset with the TSA's techniques have waged an Internet-based campaign urging people to refuse to use the scanners on Wednesday, one of the busiest travel days of the year. Coupled with bad winter weather forecasts across the Midwest, their efforts may delay Thanksgiving week travel.

In response to growing criticism, two unions representing some TSA personnel are running full-page newspaper ads Tuesday and sending e-mails defending workers to frequent fliers. While the harshest critics have suggested that enhanced pat-downs amount to sexual assault, union officials said screeners are merely carrying out orders issued by the TSA.

More than 400 of the controversial scanning machines have been put to use at 70 of 450 U.S. airports since October, though the majority of passengers are not being asked to use them. The scanners, which penetrate clothing to produce outlines of the naked human body, are in use at all three of the Washington region's major airports. In development for several years, the machines use backscatter and millimeter wave technology intended to reveal nonmetallic security threats that wouldn't be caught by traditional step-through metal detectors.

The scanners are intended to catch terrorists such as Umar Farouk Abdulmutallab, the man accused of trying to bring down a passenger jet bound for Detroit last Christmas with explosives hidden in his underwear.