BY ANDREW SABL

Remember in 1999 when two NASA planetary probes, costing about $300 million total, bit the cosmic dust? Many noted that the basic problem was NASA’s then-slogan: “Faster, Better, Cheaper.” That’s a standard engineers’ motto. But as a lot of engineers pointed out, the motto actually has a second line: “I can give you any two out of three.” Cheap products rushed out quickly have flaws; good products made quickly cost money; cheap and good products take time.

A lot of life is like that. It involves not “either-or” trade-offs between two things, but three-way trade-offs in which maximizing two things requires giving up a third. In the interesting times we may have coming, we should keep in mind that the trade-offs involving antiterrorism policy are like that too.

We’ve heard a lot about the trade-off between liberty and security. But there’s actually a three-way trade-off. It’s much easier to preserve both liberty and security if we’re willing to sacrifice a lot of privacy.

Most of what we’ve done to increase our security against terrorists involves big costs to privacy, but little, if any, cost to liberty. The FBI after Sept. 11 decided to round up hundreds of innocents and hold them as “material witnesses” because it had not had these suspects under surveillance. To get information (too late) about their intentions required personal interrogation. If the government had already found out — by scanning phone calls, intercepting e-mails and bugging houses — that most of the people it suspected never talked about terror plots, it could have avoided the mass arrests — and focused its attention on people whose actions gave some evidence that they really were terrorists.

The streets of central London have long been crisscrossed by a seamless network of TV cameras to deter and catch IRA bombers. Britons accept that — given the alternatives. Those alternatives have included, demonstrably and historically, getting blown up, and a series of police scandals in which authorities, desperate to get arrests in terror cases, arrested innocents on trumped-up charges and fabricated evidence that put them in jail — for years. The U.K. has sacrificed privacy to gain both liberty and security.

Put another way: There are a lot of things worse than having an FBI file — like being imprisoned, held without trial, tortured or killed.

The U.S. government, as The Washington Post has been reporting the last few months, is clearly doing a bit of all these things to catch potential terrorists and encouraging the secret police of less scrupulous countries to do even more. So given the alternative of letting those innocent of terrorism (or only peripherally involved) be tortured, perhaps we should feel less reluctant than some civil libertarians are to let the Homeland Security Department scan people’s e-mail to see if they’re innocent or guilty.

“Freer, Safer, More Private?” I can give you any two out of three.

Sabl is assistant professor in the Department of Policy Studies.