OKLAHOMA CITY — During a major terrorism exercise last year in which mock “dirty bombs” went off in two major U.S. cities and Guam, officials had problems working with radiation experts and relaying the extent of the damage to the public, according to a federal report released Thursday.

U.S. Department of Homeland Security officials met in Oklahoma City on Thursday for a closed-door conference with state and local emergency responders to discuss the preliminary results of the October 2007 exercise.

The report also highlights some of the strengths observed during the exercise, such as quick responses to the mock explosions, information sharing between agencies and helping special-needs populations like the elderly.

The simulated terrorist attack involved the coordinated explosion of fictional “dirty bombs” at key locations in Phoenix, Portland, and Guam to determine the nation’s ability to respond to a terrorist attack involving weapons of mass destruction.

The fourth Top Officials exercise — dubbed TOPOFF — cost about $25 million and involved more than 23,000 federal, state, local and private sector participants.

The use of “dirty bombs,” a conventional explosive with radioactive material, poses some unique problems for emergency managers responding to a disaster and providing information to the public, said Donald Hamilton, the executive director of the Memorial Institute for the Prevention of Terrorism, where Thursday’s conference was held.

“Even after you know exactly what the radioactive material is, figuring out where smoke or dust from a given place is going to go and how fast it’s going to settle is not something you can just punch into a calculator,” Hamilton said. “It’s a particularly tricky thing, and people want to know and frequently want to know with more precision than anyone can tell them.”

The report on the exercise shows there also were problems managing the incident sites, including inexperienced personnel and problems coordinating multiple missions.

DHS preparedness official Dennis Schrader said the goal of the exercise is to identify problem areas so that emergency officials are better prepared to respond to future disasters.

“The whole idea is that more real you make it, the more pressure it puts on the top officials in their participation, and then they learn and grow from that,” Schrader said. “We have some boots-on-the-ground activities ... but the real focus is on how do top officials get involved and make decisions.”

Bill McNally, the director of DHS’ exercise division, said many of the strengths observed during the drill were the result of experiences gained responding to natural disasters like Hurricane Katrina.

“From Katrina, we learned a lot of lessons that we’d have to address even in a terrorist incident, and that deals with the special needs population, elderly that might be in assisted living communities, folks that don’t speak English ... because they’re going to be victims as well,” McNally said. “We addressed all of those in this exercise, and those are some things we learned some lessons about.”

Officials also announced Thursday that the Memorial Institute for the Prevention of Terrorism, located next to the site of the Oklahoma City bombing, would be used in the future for federal training programs involving emergency management officials.

“We haven’t moved into the exact specifics of the program yet, but I would anticipate several hundred state and local officials, trainees, a year moving through Oklahoma City,” Hamilton said.