Loudoun County school officials have announced a plan to lock down schools in the event of a chemical attack. County rescue workers have readied hazardous material teams and bomb squads, and the Sheriff's Office stepped up patrols near some government buildings.

County officials said Friday that they were responding to warnings of terrorist attacks by preparing for worst-case scenarios, and they urged residents to be prepared but not to panic. Public safety officials suggested having bottled water, flashlights and a battery-powered radio on hand.

"We're instilling in everyone that this is a time when extra caution needs to be taken," said Mary Maguire, spokeswoman for Loudoun County Fire and Rescue Services.

As public safety officials braced for a possible attack, Loudoun's mental health professionals offered to help families cope with stress brought on by the terror alert. Loudoun's Resilience Project, funded after Sept. 11, 2001, through a grant from the Federal Emergency Management Agency, provides free stress management or emergency preparedness sessions for businesses or community groups.

"People are talking about it and don't really know what to do," said June Eddinger, project director. "It's frustrating. It's the fear of the unknown. It's a normal response to an abnormal situation."

Loudoun's public safety officials said that they were in close contact with other agencies in the Washington area and that there would be a coordinated regional response to any disaster in the region.

Maguire said that extra dispatchers were assigned to Loudoun's 911 center to handle any emergency and that a staffing plan was in place to call in extra workers, if necessary. Loudoun sheriff's spokesman Kraig Troxell said extra patrols are continuing in "high risk" areas during the heightened alert.

Similar precautions have been taken in Fauquier County, said Philip Myer, who heads the county's Department of Fire and Emergency Services. Myer said Fauquier was ready to open its schools if shelters were needed.

Fauquier schools Superintendent J. David Martin sent a letter to parents Wednesday, saying they should call 540-347-6195, the number used by schools to advise of snow delays or closings, to find out how schools were responding to any emergency.

"We will rely on the expertise and training of the emergency management and law enforcement officials to indicate what response is most prudent to a specific terrorist act," Martin said in the letter.

On Thursday, Loudoun school officials added a "shelter in place" procedure to their emergency response plan. The school system's previous plans, in place since 1993, allowed for schools to be evacuated or locked down with limited access.

The new plan, copies of which were distributed to principals Friday, allows schools to be sealed off and school administrators to keep children indoors.

Parents could take children out of school in all emergencies unless schools officially go into "shelter in place" mode after a chemical accident, said spokesman Wayde B. Byard. If the plan is invoked, school ventilation systems would be shut down, windows and doors secured and students sheltered indoors.

"The neutral atmospheric pressure created by these actions would help keep chemical agents from leaking into the building or portable classroom," Superintendent Edgar B. Hatrick III wrote in a letter sent home to parents Friday.

Signs would be posted on doors in English and Spanish to alert parents that schools were closed, Byard said.

In case of emergencies that do not require the "shelter in place" mode, parents should be prepared to show photo identification to take children home early. Even in those situations, parents are urged leave their children in school, where they are safe, and ensure their own safety, school officials said.

"We want the children to know we're taking this seriously, but we don't want to overreact," Byard said.

Principals said they have been reviewing disaster plans with teachers and fielding calls from parents about emergency response procedures.

"Mostly, I just need to reassure parents that, yes, we have an emergency plan in place, and, yes, we practice it all the time," said Mary L. Green, principal of Hillside Elementary School in Ashburn.

As law enforcement and rescue officials prepare for the possibility of a terrorist attack, U.S. Rep. Frank R. Wolf (R-Va.) announced that $5 million in federal funding has been set aside to establish a disaster response training center at George Mason University's Loudoun campus. Firefighters, paramedics and police officers will train there.

The Community Resilience Project of Loudoun County can be reached at 703-737-8524. The project's Web site is www.loudoun.gov/mhmr/resilience.htm.