In the U.S. military's Survival, Evasion, Resistance and Escape program, or SERE, troops are trained to prepare for possible capture by an enemy. To help them endure, trainees are sometimes subjected to one of the most severe stressors human ingenuity can devise: extreme sleep deprivation combined with an endless audio loop of a crying baby.

When used against detainees, such techniques violate international law, and even for volunteers they can be agonizingly difficult to endure. "After 36 hours, I was a total mess — I was hallucinating," one SERE veteran said.

Most parents of young infants know the feeling.

Because babies cry a lot — generally at unpredictable hours — many new parents get even less sleep than soldiers in the SERE program.

In any parenting forum, try suggesting that it won't hurt a tired baby to cry for half an hour in her crib every now and then. The backlash will be prompt.

Even pediatrician Richard Ferber, author of the 1985 classic "Solve Your Child's Sleep Problems," recently beat a strategic retreat in the face of those who consider it barbaric to let a tired baby cry in her crib.

In 1985, Ferber argued that many well-meaning parents inadvertently teach their babies to be poor sleepers. Babies like company, so if you run to them every time they emit a tiny squawk, they quickly learn that squawking pays. Next thing you know, you've got a tyke who wakes up wailing every hour, all night, every night, and won't return to sleep unless you rock him in your arms for 45 minutes while pacing the room and humming Brahms' "Lullaby."

Instead, Ferber urged, you should put the baby gently into his crib, kiss him and leave, returning, if he cries, only briefly and at progressively longer intervals. Your baby (who is smarter than you think) quickly figures out that he can't keep you around by squawking, so he decides not to bother and goes to sleep.

But in the revised edition of his book, published last week, Ferber seems to have gone on the defensive. He takes pains to emphasize that "the approaches I recommend are designed specifically to avoid unnecessary crying."

The key word there is "unnecessary." Babies who wake repeatedly during the night end up overtired and cranky, and neither Ferber nor parents willing to tolerate a little crying in the interests of sleep training should feel any need to be defensive.

Most pediatric sleep experts agree that some variant of the method popularized by Ferber is an effective and healthy way to teach babies to sleep through the night — especially when used by loving parents who combine a reassuring bedtime ritual with a keen awareness of their child's biological sleep/wake rhythms.

None of this makes sleep-training your baby easy. Humans — especially mothers — are hard-wired to respond emotionally to an infant's cries. But just because your baby cries at bedtime doesn't mean it's in her best interest for you to rush back, arms outstretched, ready to start rocking.

Think of it like this: If you take a lollipop away from a toddler, she'll cry. But if it's her sixth lollipop of the day, and she already has a mouthful of cavities, you're not doing her much of a favor if you stem the tears by offering a new lollipop.

When it comes to your baby's sleep, you're the lollipop.

What's more, it's hard to be a good parent when your nerves are shot and you're exhausted from your baby's repeated night wakings.

Sure, your baby will be happy to see you in the wee hours. But your baby needs a psychologically functional parent more than she needs your middle-of-the-night companionship.

So go ahead, parents, put your baby in the crib and give her a kiss, then put in those ear plugs and take a short nap. In the long run, you'll both be happier.