Washington - The likelihood of terrorist groups such as al-Qaida targeting chemical facilities and nuclear power plants is far greater than their ability to unleash weapons of mass destruction, policy experts said at a briefing yesterday to address potential domestic attacks.

While groups such as al-Qaida have made efforts to obtain and develop chemical and biological weapons, the federal government has produced no evidence that the groups currently possess such agents, said Elisa Harris, a chemical and bioterrorism research associate at the Center of International Security Studies at the University of Maryland, College Park. More worrisome, she said, is the idea of an attack on one of the 38,000 U.S. facilities that store dangerous industrial chemicals, such as chlorine.

"We should be less concerned about chemical weapons attacks and more concerned with preventing the chemical equivalent of the September 11th attacks," Harris said, suggesting that better warning systems be put in place in communities near such facilities.

Similar concerns exist when considering the approximately 100 nuclear power plants in the nation, said Steven Fetter, a physicist and professor of public policy at the University of Maryland center. Though nuclear weapons are both reliable and very destructive, the chances of a terrorist group obtaining such weapons are small, he said.

The "greatest overall risk" in the nuclear or radiological arena would be an attack on a nuclear facility, Fetter said, which would be equivalent to "thousands of small nuclear weapons." He suggested guards at nuclear facilities plan for more aggressive attacks than they have planned for in the past.

Experts at the briefing, which was designed to aid reporters covering nuclear, chemical and bioterror attacks, said biological attacks would most likely not be identifiable until individuals started showing up in hospitals with illnesses.

Hospitals still are learning how to deal with possible bioterror attacks, said Harold Standiford, medical director for infection control at the University of Maryland School of Medicine and Medical Center.

"We're not ready, but we're a lot closer to being ready than we were before anthrax," he said referring to the letter scare of 2001.