“The magic number was 30,” said Marc Garlasco, who was the Pentagon’s chief of high-value targeting at the start of the war. “That means that if you hit 30 as the anticipated number of civilians killed, the airstrike had to go to Rumsfeld or Bush personally to sign off.” If the expected number of civilian deaths was less than 30, however, neither the president nor the secretary of defense needed to know.

Four years later, the U.S. military still has rules in place that permit the killing of civilians in airstrikes. In fact, the number of anticipated civilian deaths is carefully appraised beforehand in a calculation known as the collateral damage estimate, which is then reviewed by commanders and military attorneys who must decide if the benefits of the strike outweigh the cost in innocent civilian lives. The military’s goal is to reconcile precision-bombing technology with the web of international treaties, including the Geneva Conventions, designed to protect civilians during wartime under a legal rubric called the Law of Armed Conflict.

But what these rules mean is that killing civilians is legal — as long as the deaths are the result of a strike at a legitimate military target. And it also means that some unknown percentage of civilian deaths from airstrikes in Iraq and Afghanistan are not accidents.

“‘Accident’ is not the right word,” said Sarah Holewinski, executive director of the Campaign for Innocent Victims in Conflict, which works to help remunerate civilians caught in the crossfire. “They call them accidental deaths, but they are not,” said Holewinski. “They know what they are doing.”

The decisions the bomb planners are making about who lives and who dies are increasingly important. While Washington’s political elite wrestles with how to wind down the ground war in Iraq, the air wars over Iraq and Afghanistan are escalating sharply. In the first six and a half months of 2007, according to a Human Rights Watch database, the U.S. Air Force dropped 527,860 pounds of bombs in Afghanistan — nearly equal to the 575,500 pounds during all of 2006, according to that database. In Iraq, the tonnage is lower, but the increase is more dramatic. In the first half of this year, 222,000 pounds of bombs fell in Iraq, compared to 61,500 during 2006.

Today, thanks to improved technology and intelligence, U.S. officials know with more certainty than ever that they may kill innocent civilians in an airstrike at a legitimate military target, like a key insurgent leader. But the same technology, they say, also permits them to minimize the inevitable civilian casualties. Col. Gary Crowder, the deputy director of the Combined Air Operations Center in Qatar, the command hub running the air wars in both Iraq and Afghanistan, calls it “precision as a method to decrease casualties rather than a method to hit the target.” Within the past two years, the military has come to recognize that collateral damage is a crucial consideration in the larger battle for hearts and minds. Is the collateral damage estimate a particularly chilling example of military bureaucracy, or is it a modern and efficient tool for saving lives?

What is happening in Iraq and Afghanistan today is a far cry from the sweeping, indiscriminate “carpet bombing” of Vietnam 40 years ago, when nobody really knew when the strings of falling bombs from massive B-52s might be landing on civilians. It’s also different from the situation in the first invasion of Iraq 16 years ago, when, despite all the publicity about “smart bombs,” 90 percent of the aerial munitions used were blunt instruments — old-fashioned, unguided “dumb bombs.” Things have even changed a lot since the invasion of Iraq four years ago, when estimates of collateral damage were crude and based on outdated information.

The transformation began with the intersection of high technology and bad publicity in the first Gulf War. The pivotal moment was the airstrike that killed approximately 288 Iraqis sheltered in the al-Firdos bunker in Baghdad on Feb. 13, 1991. After that incident the man running the war, Gen. Norman Schwarzkopf, personally reviewed every proposed target and reportedly called off some strikes. The military realized that the advent of precision-guided munitions gave it the ability to minimize collateral damage as well as increase the percentage of targets destroyed. The first Gulf War gave birth to a modern military bureaucracy that could analyze and approve airstrikes based, in part, on anticipated civilian casualties.

A dozen years later, during the opening phase of the second Iraq war, there was a system in place for calculating those casualties. In 2003, collateral damage estimates of civilian deaths from planned airstrikes were done with computer models using outdated population density statistics. There was also that magic number, 30, that required a signature from someone in Washington.

According to Crowder, there was a higher tolerance for civilian casualties during the first phase of the war than there is at present. Garlasco, now a senior military analyst at Human Rights Watch, describes a callous approach back in 2003. “It is important to understand that in January 2003 when the target packages were ‘finalized,’ we had about 300 targets that were considered ‘high CD,’ or high collateral damage, meaning over 30,” Garlasco wrote in an e-mail. “We had the Air Force play with the bomb angles, fusing, bomb tonnage, etc., and got that number down to about 25.”

Garlasco said every high-CD target was ultimately approved except two structures holding foreign journalists, the Al-Rasheed hotel and Saddam’s Ministry of Information.

The days of the “magic number” of 30 are over. The sign-off process now used to approve airstrikes in Iraq and Afghanistan is classified. But there is still methodology in place for collateral damage estimates. Planners must still ask and answer a set series of questions about each airstrike, including the number of expected civilian casualties.

The collateral damage must be proportional to the military advantage gained by the strike. “You can’t deliberately target civilians,” explained Georgetown law professor David Koplow. “But the proportionality judgment contemplates that sometimes civilians will be harmed in pursuit of a military strike.”

The number of civilian casualties is still a key factor in determining which strikes are approved and who must sign off. “That will determine who the approval authority is,” Crowder said. Strikes likely to involve higher collateral damage still require higher approval.

Four years after the invasion there is far better on-the-ground intelligence and far better technology. The skies over both Iraq and Afghanistan are filled with buzzing drones armed with powerful cameras. Military officials hundreds of miles away planning an airstrike can, in some cases, literally count the number of women and children near a target by staring at a screen. In other cases, troops on the ground calling in airstrikes can see nearby civilians with their own eyes. And individual “smart bombs” dropped in Iraq or Afghanistan are steered to pinpoint targets with stunning precision, sometimes guided by a laser shot by someone standing on the ground staring at the target.

We do know some of the details of the classified sign-off process. Many of the tough calls are made in Crowder’s command center in Qatar, 700 miles south of Baghdad. It is the brain center in control of every detail of the air wars above Iraq and Afghanistan. In the air-conditioned comfort of that command hub, Crowder’s team assemble explicit “air-tasking orders” for almost all of the airplanes flying over the two war zones. This includes targets that have been reviewed by commanders and vetted by attorneys.

There are two kinds of airstrikes. The first are preplanned strikes aimed at what are sometimes called “deliberate targets.” An example would be a bridge, a Taliban leader, or an insurgent safe house quietly under surveillance from a circling drone. The military calls this new capability to eye a target for a long time “persistent look.”

The cold, hard math of estimating collateral damage for preplanned strikes includes a calculation of the precise number of expected civilian deaths from each bomb, and it is made every day for every strike in the air wars over Iraq and Afghanistan. This grisly number is what must be weighed against the military value of the target in question. Garlasco calls that process “the macabre calculus of trying to determine how many dead civilians are worth a dead bad guy.”

Planners say they go to great lengths to minimize collateral damage. The size of each bomb, ranging from 250 pounds to the extremely devastating 2,000-pound varieties, is minimized. The direction of the approach of the aircraft is altered to focus the explosive force away from civilians. And extreme prejudice is supposed to be employed when civilians are thought to be within 1,000 feet of a target, a situation referred to as “danger close.” Military officials even consider what is on the ground underneath an approaching plane to minimize the damage in case a malfunction causes munitions to fall short of their targets. “We always look at our run-in heading and what is underneath the run-in heading,” Crowder said. “This is a constant evolution of trying to get more and more precision.”

When the assessment has been made, the planners submit the proposed airstrike to a military attorney whose job is to make sure the assessment has been done according to the law and that the anticipated casualties are within set limits.

These kinds of deliberate targets, however, represent a minority of the airstrikes in Iraq and Afghanistan. Much more common is the second category of airstrike: close air support. These are hastily arranged attacks from the air to relieve troops on the ground under enemy fire. They present a unique set of challenges with respect to protecting civilians.

Some planes are tasked to simply circle Iraq and Afghanistan, patrol air space, and wait for the troops on the ground, pinned down by enemy fire, to call for bombs. These situations are dubbed “troops in contact.”

During “troops in contact” situations, the targeting for an airstrike is done by a person called a joint terminal attack controller — the person on the ground authorized to aim the bombs. In some cases, the controller is out in the field right next to the troops in contact. And he is likely to aim those bombs using either a laser or a GPS system.

In the laser method, the controller on the ground aims the laser at the target. A pilot high above that target identifies the laser dot, and the coordinates of the dot are routed to the “smart bomb” under the nearby circling airplane. Once released, the bomb steers itself to the target.