ACCORDING TO Senate overseers of America’s intelligence community, the federal government has been collecting massive quantities of so-called metadata about Americans’ phone calls for seven years. Their revelation Thursday came hours after the Guardian published what appears to be a copy of a secret court order to a unit of Verizon, requiring the phone company to give government counterterrorism agencies information about all the calls on its network — records of originating and receiving phone numbers, the duration of calls and, it appears, cellphone location — on an ongoing basis.

One of the many things that are still unclear is why Americans didn’t know about this program on an ongoing basis.

Though the Patriot Act allows the government to seek secret court orders to obtain “business records” — a loose term that can mean “any tangible thing” — from third parties such as phone companies, the law seemed to anticipate such requests being connected to a terrorism investigation of a particular person or a set of people, not every Verizon customer. Still, the law’s language is very permissive.

Leaders of the Senate Select Committee on Intelligence explained Thursday that the Verizon order was a routine judicial reauthorization, one piece of a years-old program, about which Congress has been thoroughly briefed. Though the government, with court permission, collects a huge amount of phone metadata, government agents have to go back to court to gain access to any bit of the contents, demonstrating “reasonable, articulable suspicion that the records are relevant and related to terrorist activity,” committee Chairman Dianne Feinstein (D-Calif.) said. It appears, then, that the Verizon order represents only part of the judicial oversight to which the program is subject. The government archives the metadata but cannot trace anyone’s calling pattern without justifying the need to a judge.

But if the program is so extensive and there are two layers of court review — at the collection phase and at the access phase — why couldn’t Americans know about this process before now? The really sensitive information is not its existence — at that, ordinary Americans are probably more surprised than any terrorist is — but rather the intelligence the government uses to target individuals within the database. Also: Are all telephone companies involved? Does the government use the information for “data mining” — that is, searching for patterns that might indicate terrorist activity? It’s easy to imagine that retroactive access to phone records would be a useful tool after the National Security Agency or the FBI linked a number with a terrorist, but what have the benefits of the program been?

The Post reported Thursday night on another program, this one accessing U.S. Internet servers to collect information, ostensibly on foreigners. The apparent sweep of that program, called PRISM, also highlights the need for congressional oversight and public debate about the reach of government intelligence-gathering.

In the days after the Boston bombings, many asked why the government didn’t connect the dots on the Tsarnaev brothers. Now, many are asking why the government wants so much information about so many Americans. The legitimate values of liberty and safety often compete. But for the public to be able to make a reasonable assessment of whether these programs are worth the security benefits, it needs more explanation.