Flooded by calls from jumpy parents, Fairfax County school administrators are reshaping their message about how they would respond in the event of a chemical or biological terrorist attack.

The emergency plan, known as shelter-in-place, calls for keeping students in locked-down schools, inaccessible to parents, while teachers help undress and shower any child who needs decontamination.

In an attempt to ease parents' fears, administrators now are clarifying aspects of the plan. Children probably would be held in schools for hours, not days, and would not be showered unless their clothes were filled with harmful chemicals, officials said.

The officials also stressed that parents would be prevented from collecting their children only because no one should go outside if terrorists unleashed deadly chemicals or germs.

"A lot of misinformation is being generated around the community," Superintendent of Schools Daniel A. Domenech said, explaining why he was attempting to clear up misconceptions about the policy.

The federal government's recent decision to raise the national terrorist threat level heightened some parents' concerns and put a spotlight on what the schools were doing to prepare for a possible attack.

In an interview, and at a recent School Board meeting, Domenech said the shelter-in-place plan was not intended to cover "a matter of days, but a matter of hours. Therefore, we are not stockpiling additional water and clothes and food in schools. We have not asked our schools to get duct tape and plastic sheeting. There are a lot of rumors out there."

School district spokeswoman Kitty Porterfield added that parents would be kept away from schools "only in an environment where they could not be standing alive outside of a school either."

Letters have gone home to parents driving these points home, and school officials have set up a link on the district's Web site: www.fcps.edu/DOC/support/shelterinplace/index.htm.

The thought of being unable to see one's child during an emergency is intuitively hard to accept, several parents have said. After the attacks on Sept. 11, 2001, hundreds of Fairfax parents brought their children home before school ended.

Betty Griggs of Fairfax, who has four children in county schools, said she knew that if an attack occurred, she could not drive "to four different schools hysterically running around to get them" and was "thankful that plans are being made."

On the other hand, she said, "I hope that schools will be sensitive that it would be terrifying for the parents to be separated from their children."

Domenech and Porterfield acknowledged those fears. But they and James McLain, security coordinator for county schools, said parents should know that sometimes it is safer to keep children in schools. No one who has followed shelter-in-place procedures has died as a result of the 35 major chemical accidents in the United States in the past 20 years, McLain has said.

Eventually, school officials said, students will practice shelter-in- place procedures repeatedly and understand them.

As early as March, schools could begin run-throughs of the plan, though not actually undressing and showering students.

By fall, officials said, the exercises could become as common as fire drills.