WASHINGTON — Devices used to jam electronic signals that detonate homemade bombs in Iraq are so powerful they can "cause the loss of all communications" for U.S. troops in the area, according to Pentagon records.

That's sparked an urgent request by the Pentagon to develop a radio system that would be immune to the jammers. Electronic jammers have been a lifesaver for U.S. troops by disabling improvised explosive devices (IEDs), the largest single killer of U.S. troops in Iraq.

The jammers that protect troops from roadside bombs can blind them to communications on the location of enemies and allies. In close-quarter, urban warfare, communication can be a life-or-death matter.

"It is a nightmare," said John Pike, the director of military think tank GlobalSecurity. "Any part of the spectrum we can use to communicate is part of a spectrum that the enemy can use to detonate an IED."

IEDs have killed at least 13 U.S. troops in Iraq this month, according to U.S. Central Command. Three died Saturday in IED attacks.

The addition of 21,500 U.S. troops — most of them to Baghdad under President Bush's plan — would be complicated by poor communication. More than 1,000 troops have been killed and 11,000 wounded by insurgent bombs, Pentagon records show.

"Twice as many combat troops means twice as big a problem," Pike said.

On Jan. 4, the Pentagon posted an urgent notice soliciting information about radio systems that would not interfere with and could operate simultaneously with the jammers. Jammers make up the bulk of Pentagon spending to fight IEDs, records show. In 2006, the Pentagon spent $3.5 billion to counter IEDs, $1.4 billion of that on jammers.

The military has dealt with the communications problem for years. Troops initially kept power to jammers low enough to avoid interfering with communications, Marine Lt. Gen. James Mattis told Congress in 2005. But detonators for the bombs have grown more sophisticated, requiring more powerful jammers.

Christine DeVries, a spokeswoman for the Pentagon's Joint Improvised Explosive Device Defeat Organization — the military's lead agency in fighting IEDs — said she could not provide details on the urgency of the request. Troops used to fashion jammers from controls for electric toys.

One strategy to mitigate the effects of jamming is to regularly use different frequencies to communicate, Pike said. Refitting the radios for "anti-jamming" is expensive and time-consuming, he said.

The Army has ramped up efforts to deal with electronic communications and warfare. Since Jan. 1, each Army battalion headed to combat has been required to have an electronic warfare operator, said Col. Laurie Moe Buckhout, chief of Army electronic warfare. Rendering an IED harmless by an electronic signal will be one of the operator's responsibilities, Buckhout said.

The Army has put electronic warfare on par with learning to fire a weapon or administer first aid. Army electronic warfare operators disrupt enemy communications, ensure U.S and coalition troops can talk to one another and prevent the enemy from knowing what friendly forces are doing, Buckhout said. A large portion of their responsibilities will be dealing with IEDs.