Updated

The 23,000 people who work in the Pentagon will be given gas masks to use in case terrorists launch a chemical or biological attack against the building, officials say.

The Defense Department plans to begin handing out masks Monday to 20,000 civilian and uniformed employees who work in its headquarters, as well as some 3,000 others such as members of the press corps and staffs of shops, restaurants and the facilities in the building, officials said.

It is the latest move in a series of continually increasing security measures started after the Sept. 11, 2001, attacks in which terrorists demolished the World Trade Center and destroyed a section of the Pentagon.

At a town hall meeting Thursday, officials demonstrated use of the gas masks -- actually called "emergency escape hoods" because they protect victims for only up to the hour or so it might take to evacuate an area after a chemical or biological attack.

"In no way does it reflect some specific piece of intelligence that the Pentagon is going to be the target of a chemical event," said John N. Jester, the Pentagon police chief.

Several hundred defense employees attended the Pentagon meeting, where officials talked about security changes still planned or already instituted since terrorists crashed a plane into the five-story, five-sided building and killed 184 people.

Employees wanted to know if there is enough stockpiled food and water in the building to last out a terrorist attack (they're looking into that); how well their new gas masks are expected to work (they're the best on the market, Jester said); and what about protection for the children who employees leave at the onsite day care center every day (they've added guards and barriers and are doing "some things" he didn't want to mention for security reasons.)

Much already has been done at the 208-acre suburban Washington Pentagon property, which sits at a busy subway stop, is at the crossroads of several major thoroughfares and includes shopping, banking, cafeterias, barbers, dry cleaning and other conveniences in a building with 17 miles of hallways.

Raymond F. DuBois, manager of military installations worldwide, said the meeting was aimed at informing employees on how to respond "to an event that we hope will never take place again."

The meeting came about two weeks after President Bush decided to raise the nation's terrorist alert status from yellow to orange, the second-highest level, because intelligence officials said they had information pointing to the possibility of an imminent attack.

The $180 masks will be handed out at a rate of 500 a day at the Pentagon and the 46 other properties it leases in the Washington area, Jester said.

Other masks would be stored around the Pentagon for visitors.

Thousands of such masks also were delivered to Capitol Hill last summer for use by lawmakers, employees and tourists.

Since Sept. 11, officials have created a new 100-person office to oversee defenses against chemical, biological and radiological attacks; have stationed Humvees and military police at checkpoints outside the building and increased patrols inside and out.

There are chemical, biological and radiological sensors inside and outside the building, with samples taken and tested daily, officials said.

Entrances to the subway and bus stops have been moved farther from the building and testing and screening of packages coming into the building has been increased. There are new hallway speakers for the public address system and a computer program for announcing emergency instructions to employees if there is an attack.