The National Security Agency’s title conveys its crucial mission. And the task of protecting Americans in this era of global terrorism — also an era of wide-ranging computer and cellphone communications — demands a substantial level of electronic surveillance.

But that doesn’t justify the NSA’s sweeping seizure of the computer and cellphone records of tens of millions of Americans.

This week has brought stunning revelations on the immense scope of that invasion on Americans’ privacy. On Wednesday night, Britain’s Guardian newspaper reported the massive roundup, authorized by a judge’s secret order in April, of the records of Verizon’s American customers.

Then Friday’s Washington Post, citing a “top secret document,” reported: “The National Security Agency and the FBI are tapping directly into the central servers of nine leading U.S. Internet companies, extracting audio and video chats, photographs, emails, documents, and connection logs that enable analysts to track foreign targets.”

Under the code name PRISM, that program targets “troves of valuable intelligence” in cyber space. In a statement released Thursday night, Director of National Intelligence James R. Clapper defended PRISM as the source of “the most important and valuable foreign intelligence information we collect.” He pointed out that it is “used to protect our nation from a wide variety of threats.”

Director Clapper also decried media exposure of the program: “The unauthorized disclosure of information about this important and entirely legal program is reprehensible and risks important protections for the security of Americans.”

But what about constitutional protections against unwarranted government intrusion?

The Obama administration didn’t invent wide-ranging tracking of computer and phone records as a counterterrorism tool. The George W. Bush administration utilized it, under powers granted by the Patriot Act, after 9/11.

As a senator and 2008 presidential candidate, Barack Obama repeatedly criticized that practice. Yet during a speech Friday in San Jose, Calif., he said the current surveillance format has “struck the right balance” between security and privacy.

However, Alex Adbo, an attorney with the American Civil Liberties Union’s National Security Project, told Forbes.com on Thursday that the April order specifically targeted calls originating in the U.S.

Thus, Mr. Adbo argued: “In many ways it’s even more troubling than warrantless wiretapping [under President Bush]. ... This is also an indiscriminate dragnet. Say what you will about warrantless wiretapping, at least it was targeted at agents of al-Qaida. This includes every customer of Verizon Business Services.”

Sen. Lindsey Graham, R-S.C., tried to address such concerns Thursday, stressing the government’s life-and-death task —and good intentions. He told “Fox & Friends”: “I’m a Verizon customer. I don’t mind Verizon turning over records to the government if the government is going to make sure that they try to match up a known terrorist phone with somebody in the United States.”

Sen. Graham said that he’s “glad the NSA is trying to find out what the terrorists are up to overseas and in our country.”

Again, though, how far can the NSA — and the FBI — go “in our country” before crossing the constitutional line?

Yes, federal authorities must counter the ongoing terror threat. But Americans — including senators —also must recognize the threat that overreaching government surveillance poses to our fundamental freedoms.

The continuing challenge on this 21st century front is to how to strike the proper balance that keeps effective track of terror plots, inside and outside the United States — but also keeps our constitutional rights intact.

As Benjamin Franklin wisely wrote before the United States even existed:

“They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.”

And when the federal government conducts rampant, indiscriminate seizures of Americans’ computer and phone records, our liberty and safety are at risk.