Caught between complaints that airport screening has become too intrusive and threats of new terror attacks on aviation, Obama administration officials say they are sensitive to criticisms that security measures go too far, but they are insisting that the measures now in place are justified by the risks.

With the Thanksgiving travel crush imminent, the chief of the Transportation Security Administration, John S. Pistole, said in a statement that his agency would try to make screening methods “as minimally invasive as possible.” But he gave no indication that the agency would reverse its move to full-body scanners, now deployed in 70 of 450 airports in the United States, and physical pat-downs for passengers who object to the scans.

“This has always been viewed as an evolving program that will be adapted as conditions warrant, and we greatly appreciate the cooperation and understanding of the American people,” Mr. Pistole said.

Security officials said the new procedures were the only way to detect explosives hidden under clothing. “We cannot forget that less than one year ago a suicide bomber with explosives in his underwear tried to bring down a plane over Detroit,” Mr. Pistole said.