The case for and against a controversial $900 million airport security program was neatly summarized Thursday in an exchange between Transportation Security Administration head John S. Pistole and Rep. Mark Sanford (R-S.C.).

The background was this: About 3,000 TSA workers have been assigned since 2007 to size up passengers at airport security checkpoints and question those they find suspicious. There have been a handful of arrests from the 1.8 million people TSA sees daily, all on charges unrelated to terrorism.

Two federal reports — one by the inspector general of the Department of Homeland Security, the other delivered to Congress on Thursday by the Government Accountability Office — say there is scant proof that the Screening of Passengers by Observation Techniques (SPOT) program works to deter terrorism. The GAO recommended cutting off funding for the program, which has totaled nearly $900 million since 2007.

That led to testimony by Pistole and three others Thursday before the House subcommittee on transportation security. The members examined whether the program was worthwhile and whether it amounted to ethnic or racial profiling.

Pistole, who has grown accustomed to the wrath of Congress since taking the job three years ago, defended the program as an integral part of his attempt to shift the TSA toward risk-based assessment. It’s part of a response, he suggested, to his being called before House members and senators angered by reports that grandmothers and small children had been frisked, that full-body scanners were intrusive and that a one-size-fits-all approach was frustrating air travelers.

Pistole also has implemented a program that allows preregistered passengers to bypass some security measures, expanded it to include random low-risk passengers and launched other programs to speed flight crews and military members through security.

The essence of several House members’ arguments was captured in an exchange between Sanford and Pistole near the conclusion of the two-hour hearing. It underscored concerns both about racial or ethnic profiling and that people in stressful travel situations are more likely to look suspicious than they otherwise would.

“This notion of how do [you] get into somebody else’s head? I think it’s a very difficult place to be,” Sanford said. “So you have a system that’s set up to look for symptoms [of] stress, fear or deception, but I would ask you, Mr. Pistole, if you were a young kid that maybe got off the track at an early age, . . . you do have a criminal record, and a law enforcement fellow is standing in front of you asking you questions, do you believe you would exhibit stress or fear?”

“It all depends on the individual,” Pistole replied. “Yes, sure, potentially.”

“What if you were a staunch right-wing conspiracist with very strong anti-government leanings, you’ve posted some things that probably weren’t the best to post on the Internet, but you had the invisibility that goes with the Internet, but now you’ve got a law enforcement officer probing, asking you questions, would you exhibit stress or fear?”

“Again,” Pistole said, “it depends on the individual, but potentially, sure.”

“You’re an immigrant whose dad and mom came here illegally, would you exhibit stress or fear if someone was asking you questions?

“All situational, again,” Pistole said.

“Let’s say you’re a wife whose husband had beaten her and you’re just trying to get on an airplane and get out of town, would you exhibit stress or fear if someone was going into interrogation on some front?”

“Again, situational,” Pistole said.

“Which I think raises the point which the GAO report has brought,” Sanford said. “You go through a screening system which essentially undresses somebody, you send their equipment through radar detection and other devices. The question is, from a civil liberties standpoint, given those other tests, do you in addition have to go through a screening process based on somebody’s interpretation of what might be in your brain?”

“You raise good points, congressman,” the unflappable Pistole replied. “There’s no perfect science, there’s no perfect art of this. . . . This has been over seven years and we have screened by observation over 4 billion passengers, it actually comes out to 50 cents and in some instances 25 cents per passenger.”

“In reverse,” Sanford broke in, “you could say, a billion dollars [spent] with no results.”

“I would say there’s a result in terms of deterrence,” Pistole said.