Although the bombs manufactured by insurgents in Afghanistan tend to be more rudimentary than the ones in Iraq, they are more likely to injure and kill U.S. forces and their allies, military figures indicate.

This is in part because they are so easy to make and difficult to detect, senior U.S. officers say. Afghan insurgents also use such devices to stage complicated ambushes involving teams of bombers and gunmen.

A military task force dedicated to countering improvised explosive devices, IEDs, calculates that a casualty results from more than one of every four bombs troops encounter in Afghanistan. In Iraq, where the ratio was once one-to-one, about six bombs are detonated or cleared per casualty.

Homemade bombs traditionally have not been the weapon of choice in Afghanistan, according to members of the military's Joint IED Defeat Organization.

Schooled in the Cold War-era guerrilla war against the country's former Soviet occupiers, Afghan militants typically have ambushed their adversaries with rocket-propelled grenades and AK-47 fire, or fired rockets and mortar rounds from a distance.

But faced with a growing U.S. and NATO force, the militants appear to be taking a leaf from the Iraqi insurgent handbook, using bombs at least as often as any other type of attack, members say.

The counter-bomb organization recorded 3,594 devices used in Afghanistan in 2008, more than twice as many as in 2007. Lt. Gen. Thomas F. Metz, who commands the counter-IED effort, predicts a 50 percent to 60 percent increase this year as thousands of additional troops ordered into Afghanistan by President Obama push into areas that have long been under Taliban control.

"I believe we can do what we did in Iraq, and we can start beating the problem," Metz said.

Metz spoke to the Los Angeles Times on the sidelines of a recent conference in Huntington Beach, Calif., aimed at enlisting the help of private companies, research labs and academics in developing technology and tactics to reduce the effects of bombs.

At least 154 U.S. and allied service members have died in bombings this year in Afghanistan — four of them in a single explosion Thursday, including three Hawai'i-based Marines — compared with 34 in Iraq, according to icasualties.org. Roadside, suicide and other kinds of bombings are also the leading cause of civilian war deaths in Afghanistan, killing at least 725 people last year, according to a U.N. report.

The U.S. has poured billions of dollars into the counter-IED effort in Iraq, where the number of bomb attacks against American-led forces peaked at more than 2,500 a month in the summer of 2007. Last year, there were 9,036 incidents, according to the military's anti-bomb organization. Most attacks have been directed against Iraqi security forces and civilians since U.S. forces largely pulled out of the cities in June, military officials said.

"Iraq is an industrial society with an educated and predominantly urban population," Metz said in e-mailed comments after the conference. "Consequently, the IEDs encountered in Iraq are relatively sophisticated, with a wide variety of switches and technologies employed."

Because most Iraqi routes are paved, Metz said, insurgents hide bombs in culverts and trash piles on the side of the road, then use cell phones, hand-held radios or even garage-door remotes to set off the devices when crowds gather or a convoy rumbles by. U.S. forces have found ways to jam those detonation signals.

Afghanistan is a largely rural country with a less-educated population. Instead of radio initiators, Afghan bombers usually use command wires or crude pressure plates, which can be fashioned from two saw blades, some duct tape and scrap wire, Metz said.

The bombs are made from materials easy to find in a war zone, such as artillery shells and fertilizer. Because most roads are dirt, militants can bury the devices and leave the wind and dust to camouflage the danger.

U.S. forces are experimenting with ground-penetrating radar to spot bombs they might otherwise drive over. But, Metz said, "There is all sorts of other clutter 18 inches under the road, and trying to develop the accuracy of the radar in order to not give you the false positives is pretty tough."

The rugged, largely rural terrain also plays to the advantage of the Afghan militants, he said. Although the population is larger than in Iraq's, it is scattered across isolated valleys, surrounded by jagged peaks, giving bombers ample time and space to plant their devices.

Although the weapons are generally simple, "you don't need to be technologically sophisticated to be effective," said Col. Jeffrey Jarkowsky, who directs the counter-bomb effort in Afghanistan, known as Task Force Paladin.

Such bombs that explode under a vehicle are more likely to cause casualties than those aimed from the side of the road, he said.

Afghan militants also use suicide bombers or combine IEDs with an ambush.