WASHINGTON — Amid a growing public outcry over pat-downs and full-body scans, the head of the Transportation Security Administration appeared to soften his position on airport screening procedures today, saying they could be modified "as conditions warrant" to address privacy and health concerns.

"In all such security programs, especially those that are applied nationwide, there is a continual process of refinement and adjustment to ensure that best practices are applied and that feedback and comment from the traveling public is taken into account," TSA Administrator John Pistole said in a statement. "This has always been viewed as an evolving program that will be adapted as conditions warrant," in an effort to "make them as minimally invasive as possible while still providing the security that the American people want and deserve.

"We greatly appreciate the cooperation and understanding of the American people."

Pistole’s comments appeared to be a change in course, or at least modify comments he made earlier today when, in interview on CNN’s "State of the Union," program he said flatly that the procedures were "not going to change."

"Clearly, it’s invasive; it’s not comfortable," he said in the television interview. But "no, we’re not changing the policies ... because of the risks that have been identified. We know through intelligence that there are determined people, terrorists who are trying to kill not only Americans but innocent people around the world."

Pistole conveyed similar sentiments last week in testimony before the Senate Commerce, Science and Transportation Committee.

Pistole’s boss, Homeland Security Secretary Janet Napolitano, may be able to shed light on his comments today when she appears with Sen. Frank Lautenberg (D-N.J.) at the Trenton Train Station to promote a public awareness campaign for rail travel.

Critics have derided the full-body airport scanners as "virtual strip searches," for their ability to see through passengers’ clothes, and called the more aggressive pat-downs "gropes" and even legalized "sexual assault," after complaints of screeners touching passengers’ genitals.

The website www.optoutday.com is calling upon air travelers to boycott scanners at airports around the country on Wednesday, traditionally one of the busiest travel days of the year. The scanners are optional, though passengers face an automatic pat-down if they opt out.

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Pistole has called the movement "irresponsible."

Last Friday, Rep. Rush Holt (D-12th Dist.) sent Pistol a letter requesting a meeting and insisting that "our airline security screening system is broken."

Holt, a trained physicist who co-chairs the Congressional Biomedical Caucus, hosted a congressional forum last March during which he raised concerns over radiation emitted by the X-ray backscatter scanner used at JFK and other airports. (Newark uses so-called millimeter wave scanners, which have not raised the same concerns.)

"As a scientist and the chairman of the Select Intelligence Oversight Panel, I appreciate the challenges we face in trying to prevent terrorists from boarding American airliners," Holt’s letter to Pistole said. But, it said, "TSA’s current obsession with fielding body imaging technology is misguided, counterproductive, and potentially dangerous."

Earlier last week, a bipartisan group of New Jersey legislators urged Congress and President Obama to address health and privacy concerns over the scanners and pat-downs.

Obama addressed the issue in Portugal on Saturday, telling reporters he had asked the TSA to look into less intrusive screening methods.

"I understand people’s frustrations," the president said.

Today, Secretary of State Hillary Clinton made the rounds of the Sunday morning talk shows, telling NBC’s "Meet the Press," the administration was trying to strike "the right balance" between privacy and security.

Asked on CBS’ "Face the Nation" if she would submit to a pat-down, Clinton replied, "Not if I could avoid it. No. I mean, who would?"