"What if by using torture against an al Qaeda operative, U.S. forces were able to prevent a significant terrorist attack and save hundreds or thousands of American lives," a reader wrote to The Post in a letter published Friday. "Should torture be authorized?"

It's a seemingly simple question, one that many of us asked ourselves in the days and weeks after Sept. 11, 2001. Back then, the answer seemed relatively simple, too: If you could save, say, 3,000 lives by subjecting one terrorist to harsh or even painful interrogation methods, how could that not be the moral thing to do?

Now, after months of disturbing revelations about prisoner abuse and prisoner homicide by U.S. soldiers and interrogators, is the answer still simple? Many would say yes -- would say, as the letter writer was suggesting, that we cannot afford to be squeamish in the midst of a war on terrorism. Because the United States has been spared further attacks at home, they would say, we moralists may delude ourselves into thinking that we can once again afford the luxury of pure principle and uncompromised civil liberties. But let terrorists strike again -- perhaps more catastrophically than before -- and we will once again put the Geneva Conventions into proper perspective.

It's a useful challenge to critics of the administration. There is a danger of complacency as Sept. 11 recedes, and anyone who pretends that the answer on torture is easy probably has never borne the burden of protecting the nation from attack.

But I think something more than the passage of time has happened since we asked ourselves the is-torture-ever-justified question nearly three years ago. We're beginning to see that it may not be possible, once you accept the moral legitimacy of torture, to limit it to those rare circumstances that we may have had in mind. And this is not because there will always be a few sadists or bad apples who push the limits. It's because there will be many good apples, true patriots, who believe they have an obligation to take every step legally available to them to fulfill their duty and protect their country.

Imagine, for example, that you are a general in Iraq, watching as several of your soldiers are killed or maimed every day by roadside bombs. You are frustrated by how little you know about the enemy and by how little you are learning from prisoners you have captured. In the old days -- that is, before the second Bush administration -- you nonetheless knew that you could not subject prisoners to "force, mental torture, threats . . . [or] inhumane treatment of any kind," as a Defense Department analysis of interrogation law explained a year ago. But if, suddenly, the old rules do not apply, can you responsibly not threaten your prisoners with dogs or shackle them to bedposts, if there's a chance it may save American lives?

Because the administration seeks to obfuscate rather than inform and because congressional oversight has been so anemic, there is still much we don't know about the U.S. torture scandal. President Bush will say only that he has followed the law. "That ought to comfort you," he told reporters last week.

It cannot comfort us, though, because we have read the leaked Defense Department memorandum arguing (in March 2003) that no law banning torture or regulating interrogation can bind the president when he is operating in his role as commander in chief. So he may authorize abuse and still believe he is, as he said, adhering to the law.

Has that happened? We don't know. We know the administration has decided that sizable numbers of captives won't be protected by the Geneva Conventions. We know it has approved interrogation techniques that are degrading, painful and inhumane. We have seen how these techniques have seeped from one theater of war to another. We know that abuse has been widespread, that homicides have gone uninvestigated and that prisoners have been tortured: not just abused, not just humiliated, but tortured.

We know some of the costs: that Iraqis have suffered, that the United States has lost much of its moral authority, that dictators everywhere who use national security as an excuse to torture their opponents are delighted and emboldened. We know the danger has grown for American soldiers, both those who might fall into enemy hands and those who are struggling to convince ordinary Iraqis that the United States is fighting on their behalf. What we don't know yet is the cost, to individual officers and to institutions, of blurring moral lines that the Army for decades kept clear.

After Sept. 11, many of us might have answered the letter writer's question by saying: Yes, there may be a time, an exceptional case, when the president should assume responsibility and give an order to torture a prisoner to save thousands of lives. It would be an awesome responsibility, and maybe it would be wrong, but those are the choices leaders must face.

Instead, we see a president who ducks responsibility and gives lawyers' answers. And the difficult choices are kicked down the chain of command, where they do not belong.