Heretofore, I have refrained from commenting on the so-called "domestic spying" controversy because I felt the issue involved technological aspects that couldn't (or at any rate hadn't) been disclosed for security reasons, and, without understanding which, no reasonable conclusion on the matter could be reached.

The issue came to public attention when The New York Times, after sitting on the story for a year, disclosed it because the newspaper was afraid it was going to be scooped by a book about to be published by one of its own reporters, James Risen. The gist of the charge was that the Bush administration had been reading and/or listening in on communications (letters, e-mails and phone calls) between individuals, one in this country and one abroad, one or both of whom were suspected to be working with Al Qaeda or some other terrorist organization. The problem was that Congress, in the late 1970s, had passed the Foreign Intelligence Surveillance Act (FISA), which authorized the government to monitor domestic communications, provided it first sought and obtained permission from special courts established to rule on such requests. In the particular category of communications described above, however, the Bush administration had not asked FISA's permission first.

Had it therefore broken the law, and violated the general rule against governmental eavesdropping on private communications? The Democrats promptly alleged that it had, and called the practice "domestic spying." We were supposed to believe that the government was unlawfully listening in on conversations between American citizens in Dubuque and their friends and relatives in London or Paris, with Lord-only-knows what consequences for our sacred right to privacy.

The Bush administration insisted that, on the contrary, it was only engaged in "terrorist surveillance" and was interested solely in communications that might foreshadow future terrorist attacks like Sept. 11, or worse. And the only reason it hadn't asked for permission from a FISA court first was that, thanks to modern technology, such monitoring simply had to be done too quickly to accommodate the delays inevitable in going to court.

The trouble was that neither the administration nor the Democratic leaders in Congress and their ranking members on the Senate and House intelligence committees (all of whom had been briefed by the administration on what it was doing) felt comfortable explaining publicly why everything allegedly had to be done so rapidly. Evidently, the explanation would reveal to the public (and hence to the terrorists) various secret techniques used by the government in the course of surveillance. So it was effectively impossible to explain why the administration had refused to seek court permission first.

Now, however, there is a ray of light on this crucial question. In a review of Risen's book in the Feb. 5 issue of The New York Times Book Review, Walter Isaacson, president of the Aspen Institute, states that the criticized program "involves electronically scanning hundreds of calls and e-mail messages."

He doesn't specify a time frame, but it is reasonable to assume that we are talking here about hundreds of messages per day, or even per hour. No doubt the vast majority of such messages turn out to be innocent, but this cannot be known until they are scanned. And what the Democrats are contending is that the administration ought to have sought prior permission from a FISA court to scan each individual message (or at least to have done so, as the law allows in emergencies, within 72 hours after the scan).

This is obviously impossible. Even if our intelligence officials could somehow isolate every communication between someone here and someone abroad, and bring each individually to the attention of a FISA court to seek approval for monitoring it, doing so would inevitably take many hours, by which time the communication would long since be over. And even with a 72-hour grace period in which to obtain retroactive approval, the burden of ruling on each of the thousands of applications would quickly overwhelm the court.

This overview of the practicalities, moreover, almost certainly understates the problem. Undoubtedly, there are further technological complications we have not yet so much as glimpsed. But it seems plain that we must either allow our government to monitor possible terrorist communications when they occur, or witness their consequences at our leisure.