The House Intelligence Committee, which oversees the National Security Agency’s program to acquire the telephone call lists of Americans, held a hearing Tuesday entitled “How Disclosed NSA Programs Protect Americans, and Why Disclosure Aids Our Adversaries.”

It would have been more reassuring if the hearing had been entitled: “Strengthening Oversight of NSA Programs and Preventing Abuses of Sensitive Information.”

Army Gen. Keith Alexander, the head of NSA, told the committee that “more than 50” terror plots were thwarted by a program to collect telephone call and email lists and another to listen in on calls to the United States by suspected terrorists. Under questioning, he said that the programs provided unique clues in about half of the cases, and that only 10 had involved threats to the United States.

Gen. Alexander, committee Chairman Mike Rogers, R- Mich., and ranking Democrat C.A. Dutch Ruppersburger of Maryland, praised administrative steps taken by NSA and a special secret court created to prevent surveillance abuses. For example, Gen. Alexander said the database of phone records compiled by the agency can only be accessed by 22 people, under strict guidelines. The court is regularly informed of NSA activities.

But the hearing also raised questions about the effectiveness of these protections. It brought to light the fact that the NSA apparently does not know how Edward Snowden, the former analyst who disclosed the surveillance programs, got access to his information. He did not, according to Gen. Alexander, have the necessary electronic “keys.”

And how did Mr. Snowden get the necessary security clearance for his job?

In another indication that all is not watertight in the NSA’s administrative safeguards, Gen. Alexander told the hearing that until now, systems administrators like Mr. Snowden were not carefully monitored. The NSA is now planning to require that systems administrators work in pairs.

But Thursday brought the revelation, based on a Justice Department document, that NSA analysts are indeed permitted to read and retain emails of U.S. citizens under a number of different circumstances without a court warrant. That adds concern, especially in light of assurances from President Obama and high officials of his administration that the NSA does not listen to phone calls or read emails without a court order.

These questions raise an alarm about the quality of the NSA safeguards and of congressional oversight of the agency and its massive data sweeps. Other NSA whistleblowers have said they could not get a hearing from Congress.

The surveillance programs might be valuable tools for protecting Americans, as President Obama has declared. But they are certainly not “transparent,” as he has claimed.

Congress controls the purse strings of the intelligence community. It can sunset legislation authorizing intelligence activities. It has all the tools it needs to conduct vigorous oversight. The NSA scandals are a sign it has not been doing its job.