President-elect Obama’s announcement of his (mostly) stellar national security team coincides with the release this week of a bipartisan commission report with this chilling assessment of the most important challenge that team faces: "Without greater urgency and decisive action by the world community, it is more likely than not that a weapon of mass destruction will be used in a terrorist attack somewhere in the world by the end of 2013."

Perhaps the commission, former Defense Secretary William Perry, and other experts who have issued similarly dramatic warnings are crying wolf. Perhaps the likelihood of any terrorist group getting a nuclear bomb is "vanishingly small," as Ohio State political science professor John Mueller has forcefully argued. Or perhaps it’s closer to 30 percent over the next 10 years, as Matthew Bunn of Harvard’s Kennedy School estimated last month in "Securing the Bomb 2008."

Our way of life may well depend on catching nuclear or biological terrorists before they can strike.

Whatever the odds, if terrorists ever smuggle a crude, Hiroshima-sized nuke into, say, Manhattan, the immediate death toll could exceed 500,000. And the ensuing panic could threaten our constitutional system, spur evacuations of major cities, kill international trade, bring the worst economic depression in history, and perhaps usher in a new dark age worldwide.

This prospect puts into perspective the efforts of many human-rights activists, Obama supporters, and journalists to weaken essentially all of the government’s most important tools for disabling terrorists before they can strike.

Wiretaps? These folks would make it far easier for terrorists to escape detection, by greatly narrowing the government’s electronic surveillance powers. Data mining through reams of commercial records in search of terrorist trails? Ditto. Detention of suspected "enemy combatants" who are very dangerous but cannot be criminally convicted? Release them! Interrogation of terrorist leaders? Just say no, even to mild forms of coercion such as angry yelling and threats. The USA PATRIOT Act? Repeal key provisions. FBI guidelines? Ban the feds from focusing more investigative resources on young Arab men from overseas than on African-American grandmothers.

Civil libertarians are rightly outraged by the brutality of some Bush administration interrogation methods; by Bush’s denial of fair hearings to hundreds of suspects at Guantanamo and elsewhere who claim that they are not terrorists; and by his years of secretly and perhaps illegally defying — rather than asking Congress to amend — the badly outdated Foreign Intelligence Surveillance Act.

But the civil libertarians’ outrage does not stop there. Indeed, the prospect of anyone in the U.S. being inappropriately wiretapped, surveilled, or data-mined seems to stir the viscera of many Bush critics more than the prospect of thousands of people being murdered by terrorists. This despite the paucity of evidence that any innocent person anywhere has been seriously harmed in recent decades by governmental abuse of wiretapping, surveillance, or data mining.

On these and similar issues, Obama will have a choice: He can give the Left what it wants and weaken our defenses. Or he can follow the advice of his more prudent advisers, recognize that Congress, the courts, and officials including Attorney General Michael Mukasey have already moved to end the worst Bush administration abuses — and kick the hard Left gently in the teeth. I’m betting that Obama is smart and tough enough to do the latter.

This is not to suggest that the president-elect will or should condone torture, bypass Congress, disregard international law and opinion, or adopt other Bush excesses that Obama and Attorney General-designate Eric Holder have assailed. But Obama does need to claim and use far more muscular powers to avert catastrophic loss of life and protect our security than most human-rights activists (and most Europeans) would allow.

The recommendations in the 112-page report quoted above — issued by the congressionally established Commission on the Prevention of Weapons of Mass Destruction Proliferation and Terrorism — focus mainly on the need for greater efforts to prevent WMD from falling into terrorist hands. Such efforts are critical, but at best cannot eliminate the threat. So our way of life may well depend on catching nuclear or biological terrorists before they can strike.

And the only way to catch them is through aggressive use of wiretaps, data mining, searches, seizures, other forms of surveillance, detention, interrogation, subpoenas, informants, and, sometimes, group-based profiling. Many of these powers and techniques are still tightly restricted by the web of legal restraints and media-driven cultural norms that were developed in sunnier times to protect civil liberties — and would be even more tightly restricted if civil libertarians had their way.

I sketch below how Obama should strike the liberty-security balance in three areas; in future columns I will focus on these and related issues in more detail.

• Wiretapping and data mining: Civil libertarians and most congressional Democrats have complained that the government has too much power to intercept phone calls and e-mails in search of terrorists, under the amendments to the Foreign Intelligence Surveillance Act that were adopted this summer. In fact, the government still has too little power to intercept communications and at the same time too few safeguards against misuse of the information.

FISA, which has always required judicial permission based on "probable cause" to target calls and e-mails between parties inside the U.S. but not calls from or to targets outside the U.S., is badly outdated: It is often impossible to tell where the parties to a cellphone call or an e-mail are. In addition, "the surveillance it authorizes is unusable to discover who is a terrorist, as distinct from eavesdropping on known terrorists — yet the former is the more urgent task," as Judge Richard Posner has written.

Obama, a harsh critic of Bush’s secret, unilateral defiance of FISA’s rules from 2001 through 2005, wisely broke with most liberals by voting in July to relax those rules. He should propose a complete overhaul and simplification of the almost incomprehensibly complicated law. It should be easier to use sophisticated computer data-mining programs to fish through millions of calls and e-mails for signs of possible terrorist activity. At the same time, privacy protections should be improved by tightening the rules to detect (through use of audit trails) and prevent unnecessary dissemination or retention of the intercepted information and to punish severely any misuse of it. An additional privacy protection, suggested by Posner, would be to forbid use of this information for any purpose (including, say, tax fraud prosecutions) other than to protect national security.

• Detainees: Obama should keep his promise to close the Guantanamo prison camp, within a year if possible, and should release as soon as possible and urge Congress to compensate all detainees who are found to be both nondangerous and nonprosecutable. Although Guantanamo is now about as humane as a prison housing some extremely dangerous terrorists could be, its ugly history has made it a worldwide symbol of detention without due process and brutal treatment of detainees, including many mistakenly captured innocents. Obama should also end Bush’s misbegotten system of "military commissions" to put detainees on trial for suspected war crimes, and instead should try as many as possible in ordinary military or civilian courts.

But Obama should spurn the clamor from the Left to simply release any and all of the more than 240 remaining detainees who cannot be criminally convicted. Instead, he should establish a blue-ribbon, bipartisan commission to study all the available evidence on each detainee. Many may turn out to be both extremely dangerous and impossible to convict of crimes, as the military claims, because of strict rules of evidence and other obstacles. Obama should continue to detain that group, probably in U.S. lockups, while working with Congress to establish a new process to give these men every possible opportunity to challenge the factual and legal bases for their continued detention.

• Interrogation: Obama should promptly issue an executive order reinforcing the criminal ban on torturing detainees and imposing a general rule against harsh methods. He should also direct the Justice Department to revoke or revise any as-yet-unrevoked legal opinions taking an unduly narrow view of the anti-torture law. But for reasons discussed in my May 3 column, he should preserve the option of using coercive methods short of torture in especially urgent cases, if the attorney general personally approves. And he should ask himself: What would I want done if the CIA captures another terrorist mastermind such as Khalid Shaikh Mohammed, who is determined not to talk but whose secrets — if extracted — might well save many lives?

If Obama strikes judicious balances between security and liberty, the ACLU and its allies may hysterically accuse him (as they would certainly accuse any Republican president) of trashing the Constitution. But the vast majority of voters understand that the Constitution is not a suicide pact.

Meanwhile, like the prospect of a hanging, the prospect of a terrorist nuclear bomb obliterating downtown Washington — including the Obama family — or Manhattan will concentrate the president-elect’s mind wonderfully.

This article appeared in the Saturday, December 6, 2008 edition of National Journal.