Nearly 40 percent of the U.S. soldiers who have died in the war in Iraq were killed in incidents unrelated to direct enemy fire, according to casualty patterns from the three weeks of fighting leading to the fall of Baghdad and its immediate aftermath.

The Defense Department has said that 19 of the 108 deaths among U.S. troops as of last evening were the result of accidents. A closer analysis, based on Pentagon sources and information the military is sharing with soldiers' families, indicates that of the total who have died, Iraqis killed 68, at most.

Although several of the deaths remain under military investigation, the information that can be gleaned to date offers the fullest portrait of deaths that have occurred so far. It suggests that five soldiers were killed in friendly fire incidents, three died from random causes and at least a dozen men identified by the Pentagon as killed in action actually perished at times and in places devoid of combat.

This pattern of U.S. casualties -- relatively low overall, but high in deaths outside battle -- echoes tendencies that first became evident during the Persian Gulf War of 1991, when fully half of the 300 deaths among U.S. troops were from accidents and other noncombat causes. But it also reflects changes that have taken place since then, primarily in the U.S. military.

The current conflict, like the 1991 war, has produced remarkably few U.S. deaths, compared with most wars in American history. The casualties in the invasion that began last month include 108 dead, 14 captured and missing and 399 wounded, in the Pentagon's most recent public count, out of about 250,000 troops. That is about 1 of 480 soldiers deployed in the war. From World War I through Vietnam, the ratio of casualties hovered consistently at about 1 of 15 soldiers. The casualties in the current conflict would be lower except for a single day -- March 23 -- when 22 members of the U.S. forces were killed near the southern Iraqi town of Nasiriyah and an additional seven were left missing in action. Compared with those of U.S. troops, Iraqi military casualties are thought, conservatively, to number several thousand. But firm numbers are impossible to ascertain because the U.S. military says it makes no attempt to calculate such figures.

The lower overall U.S. casualty rate, experts said, reflects improvements in military technology in the past decade, particularly more sophisticated surveillance and more precise long-range weapons. "It's a combination of being able to detect where the enemy is and being able to reach out and kill them," said retired Lt. Gen. Theodore G. Stroup Jr., a former chief of Army personnel.

"The optimists who were predicting light casualties thought they would be light because there wouldn't be any urban warfare," said Stephen Biddle, a professor of national security studies at the Army War College. "We got urban warfare without the heavy casualties."

Instead, there have been deaths that reflect the peripheral hazards of war.

Cases in point are evident among the dozen or so men who were listed as killed in action but who lost their lives where no fighting was underway.

They include a pair of Marine reservists who drowned March 24 while crossing the Saddam Canal to help secure land for a water purification team. And three Marines killed March 30 when their Huey helicopter crashed on takeoff in southern Iraq after refueling. And an additional four Marines, missing for days, who were discovered by divers 20 feet deep in the Euphrates River along with their tank, which apparently had plunged off an unfinished bridge the night of March 25.

"All I've heard is they were not under fire," said Barbi Schneckloth, a travel agent in Davenport, Iowa, whose fiance, Sgt. Bradley S. Korthaus, 28, drowned in the canal. "I just feel like he was stolen from us," she said, adding that military representatives had told his family that four members of his unit -- two of whom survived -- waded into the water without flotation devices or safety lines.

A detailed analysis of all 108 deaths, based mainly on information in official Pentagon announcements, shows that each branch of the service has lost members, but that the Army and Marines have lost the most. The Army accounts for slightly less than one-third of the troops that have been deployed but nearly half of the deaths so far. Similarly, the Marines account for a third of the deployments but 40 percent of the deaths.

Nine members of the military reserves, called up for wartime duty, have been killed, including Korthaus and Cpl. Evan T. James, 20, of LeHarpe, Ill., who drowned with him while attempting the canal crossing. Two days after the war began, an Army reservist, Spec. Brandon S. Tobler, 19, less than two years out of high school in Portland, Ore., died in a supply convoy during a sandstorm when the Humvee in which he was riding slammed into the vehicle just ahead.

At the same time, officers accounted for one death in five -- a large share, compared with past wars, caused in part by the fact that several helicopters, invariably containing men of officer rank, have crashed.

Women have largely been spared. The only female soldier to die was Pfc. Lori Piestewa, 23, a member of the Hopi Indian tribe who was missing, and then found killed, after an ambush of an Army maintenance company on March 23, the war's deadliest day for U.S. troops.

In many ways, the mosaic of casualties is a microcosm of the country: The soldiers who have died came from 36 states, including two from Maryland and four from Virginia, though none from the District. About 40 percent of the troops who have been killed came from the South, reflecting that region's relatively large presence in the military overall.

Of the 80 whose race could be determined, about one-fourth were black -- compared with about one-fifth of the military and about 12 percent of the U.S. population. At least 13, or about 16 percent, were Hispanic, compared with about 9 percent of the military and 12 percent of the country.

Ten of the dead were still teenagers, and seven were over 40.

"It's who's paying the price and who is in the military," said Christopher A. Lawrence, executive director of the Dupuy Institute, a small think tank that researches armed conflict.

Among the most intriguing patterns to emerge from the current war, however, are the ways in which troops have been killed -- ways that are not always immediately evident from the Pentagon's initial public statements.

Each branch of the service determines whether a casualty is labeled as occurring by accident or in combat, and so far, defense officials say, the services are using a broad definition of "killed in action." One Pentagon official said that any incident under investigation is categorized as a combat death until proven otherwise.

This decision, in part, reflects the military's belief that relatives would rather learn that a soldier was killed in combat than by someone's mistake, said Jeffery Charlston, an Army historian who tracks casualty issues.

And, certainly, information the Pentagon has released to news organizations and families suggests that more than half of the deaths so far in Iraq have been caused by hostile action, ranging from a car bombing to firefights.

Sgt. 1st Class Paul R. Smith of Tampa was killed on April 4. According to an account by "60 Minutes II," the 33-year-old Army platoon leader grabbed the machine gun on an armored personnel carrier and began firing at Iraqi soldiers to enable the men he supervised to escape. They did, but he was killed.

In five instances, the military has said it believes the deaths came by friendly fire.

Army Capt. Edward J. Korn, 31, of Savannah, Ga., was inadvertently shot by U.S. forces April 3 after he walked over to inspect an Iraqi tank that his unit had destroyed.

Army Pfc. Jason M. Meyer, who turned 23 last month and marked his first wedding anniversary less than two weeks ago, was killed by shrapnel on Tuesday at the main airport on the outskirts of Baghdad.

His mother, Kathy Worthington, said the officers who arrived at her home in Howell, Mich., late that night to deliver the news "said he was in a tank or on a tank, but they never said it was friendly fire." Later in the week, a Pentagon source said that it was, indeed, such an incident, because a U.S. tank round that had been fired through an airport building ricocheted off a tank he was standing next to and hit him.

In a few cases, military officials have reclassified casualties that they first said were accidental. The Marine Corps originally listed as an accident the April 2 electrocution of Lance Cpl. Brian E. Anderson, 26, of Durham, N.C. It occurred, the Pentagon said, west of Nasiriyah when the .50-caliber weapon he was manning on top of a 7-ton truck became entangled in low-hanging power lines. More recently, a Pentagon official said the Marines plan to categorize him as killed in action, because his reconnaissance battalion was traveling to a battle zone.

Soldiers' parents have found that details of their children's deaths arrive in increments.

At first, Kem Bales, the father of Pfc. Chad E. Bales, was told by a casualty assistance officer merely that his son had been killed on April 3 in a convoy accident, possibly during a period of blowing sand. The father thought he would find solace in the knowledge of a simple fact: Was Bales, 20, who had been part of a transportation support battalion, the driver or a passenger when he died? Perhaps he was a passenger, his father reasoned, because the young man had complained to his grandmother during a recent phone call from Kuwait that he was not allowed to drive certain vehicles there because he was not yet 21.

The next day, "we got just a little bit more information," Kem Bales said from his home in Muleshoe, Tex. It had been a 13-vehicle convoy. His son was in the 11th vehicle. A few days ago, he said, the Marines told him at last that his son had not been the driver.

The cause of other deaths has become more obscure as days have passed. The first Pentagon notice of the helicopter crash that killed Marine Capt. Travis A. Ford, 30, and Marine Capt. Benjamin W. Sammis, 29, said that it apparently "was not a result of hostile fire." Both families were told that the Super Cobra appeared to have crashed into a tower, perhaps unlighted, about 30 miles southeast of Baghdad just after midnight on April 4.

Since then, Ford's brother, Alex Ford, said he has heard there may have been enemy fire in the area. And in the darkness and smoke, pilots who were nearby may have had different perceptions of what took place, he said.

A Marine reservist himself, Alex Ford knows that the Marines are conducting two investigations, examining the aircraft and interviewing witnesses.

Eventually, he believes, he will know what happened. But, he asked: "Does it bring him back?"

Staff researchers Lucy Shackelford, Madonna Lebling and Margaret Smith contributed to this report.

Marines carry the casket of Staff Sgt. Donald C. May from St. Augustine Catholic Church in Richmond on Friday. May was killed March 25 in Iraq.Members of the Army's Honor Guard salute the casket of Spec. Brandon J. Rowe at Hononegah Community High School in Rockton, Ill., yesterday. Rowe was with the 101st Airborne Division.