WASHINGTON — Roadside bomb attacks and fatalities in Iraq are down by almost 90% over the last year, according to Pentagon records and interviews with military leaders.

In May, 11 U.S. troops were killed by blasts from improvised explosive devices (IEDs) compared with 92 in May 2007, records show. That's an 88% decrease.

Military leaders cite several factors for the drop in attacks and deaths. They include:

•New vehicles. Almost 7,000 heavily armored Mine Resistant Ambush Protected (MRAP) vehicles have been rushed to Iraq in the last year. "They've taken hits, many, many hits that would have killed soldiers and Marines in uparmored Humvees," Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, said in a recent interview.

Defense Secretary Robert Gates made obtaining at least 15,000 MRAPs his top priority last year.

•Iraqi assistance. Ad hoc local security forces, known as the Sons of Iraq, have provided on-the-ground intelligence to U.S. forces looking for IEDs, said Maj. Gen. Rick Lynch, who commanded a division in Baghdad from February 2007 until May.

Each member of the security forces earns about $8 per day. Lynch has hired about 36,000 of them to man checkpoints and provide intelligence on the insurgency. He said about 60% had been insurgents.

•Improved surveillance. Lynch said troops used security cameras that could see bomb builders up to 5 miles away. "If they're out there planting an IED, we can go whack them before they finish," he said.

Also, Lynch said, the 14-ton MRAPs have forced insurgents to build bigger bombs to knock out the vehicles. Those bombs take more time to build and hide, which gives U.S. forces a better chance of catching the insurgents in the act and then attacking them.

Among the new U.S. tactics, paying the Sons of Iraq is a particularly good investment, said Dakota Wood, a military analyst at the Center for Strategic and Budgetary Assessments. Whether the money is viewed as "buying off" insurgents is less important than the lull in violence it creates, Wood said. It's almost impossible to rebuild infrastructure, foster commerce and set up elections when streets are unsafe, he said. "Any effort that creates a window of opportunity in which other stabilization actions can take root is a good thing."

Iraqi insurgents, however, are changing their tactics. During a visit to the Marine Corps Air Ground Combat Center at Twentynine Palms, Calif., Marines showed Mullen the latest trend in IEDs: fake curbs fashioned from metal, filled with ball bearings and explosives. Virtually indistinguishable from concrete rubble, the new bombs require a trained eye to spot.

Insurgents are also using pressure-detonated IEDs, including those with 15 pounds of explosives that blow the tires off an MRAP and allow insurgents to attack it, Mullen said. "The whole issue of IEDs — vehicle-borne, suicide, you name it — is going to be the weapon of choice, and I think it's going to be around a long, long time," he said.