The scenario that many people had managed to push from their minds -- that terrorists would launch an attack on Washington, separating families and creating havoc -- came creeping back yesterday. For proof, one had only to visit the paint department of a local hardware store.

There, plastic dropcloths were being evaluated with one aim in mind: Would they work to seal a room?

A day after federal officials urged Americans to prepare their homes in case of a biological, chemical or radiological attack, and four days after the nation's threat level was raised from yellow to orange, many Washingtonians found themselves on a grim shopping trip, just in case.

Strosniders Hardware in Bethesda had been cleaned out of plastic sheeting by early afternoon and had called for a replacement shipment. People were stocking up on flashlights, first-aid kits and water as well, said manager Craig Smith.

"It seemed like a few were legitimately panicked," he said. "Others were calm, and others were laughing. But even the ones that were laughing were trying to get whatever they could," he said.

At the Home Depot in Fairfax City, a display near the entrance was marked by a big orange sign with black letters: Safe Room Supplies. The store was doing a steady, brisk business in its makeshift homeland security supply department, which consisted of wood pallets piled waist-high with boxes of bottled water, duct tape, rolls of plastic and, a few feet away, a rack of batteries.

Tom Rogers of Oakton was buying water, tape and plastic. He has one child, and his wife is due to deliver a second any day. He said he and his wife had picked out the highest room in the house as their safe room.

"I think everyone is really concerned about this," he said. "Last year when they raised the alert, it was vague, and the sense was it was issued just because it was the anniversary of 9/11. This time there seems to be more details about a possible threat."

While Washington has lived under a nagging cloud of fear since the Sept. 11, 2001, attacks, many residents said this week's warnings were more powerful because they were more specific.

On Monday, federal officials singled out Washington and New York as possible targets and offered more detailed advice to citizens. Recommendations included assembling disaster kits with flashlights, radios and food and water to last three days and having duct tape, plastic and other supplies to seal off a room at home.

Elias Gallardo, 62, was among those who were reevaluating as a result. He spent time last week translating the terror alert into Spanish for his co-workers at the U.S. office of the Chilean Air Force. By yesterday, he was among those he never thought he'd join: the emergency shoppers.

"This is the first time," he said with a shrug at the Pentagon City Costco, his cart loaded with bottled water and tuna fish. "I've never been worried about it before. . . . It's getting to me, maybe." It was getting to him so much, he said, that after 34 years in the United States he was thinking of going back to Chile with his wife.

Many others, however, said that despite the seriousness of the latest warning, they would not be changing their behavior unless the information became even more specific -- or they saw more evidence that precautions were likely to make a difference for them.

"If there was a credible threat of sarin gas in the Metro system, because there had been a lot of sarin stolen, I might not take the Metro," said Marc Laitin, 29, as he waited for a train at the McPherson Square station. He speculated that the heightened terror alert might be a way for the federal government to gain support for its domestic security policies.

Margaret Flickinger, 35, of McLean said she had decided long ago to make sure her cell phone is always charged, and her family has a plan for where to go if the area was evacuated. But she said she is determined to stay calm -- and had not joined the emergency-minded crowds at the hardware and grocery stores.

"I'm not panicking," said the mother of two boys, 5 and 2. "If I get panicked, my children get panicked."

Government agencies were responding to advisories in their own ways yesterday.

Metro Transit Police increased patrols with its 11 bomb-sniffing dogs, said Chief Polly Hanson. Officers have been assigned to the busiest stations during the morning and evening rush periods, instead of having them roam several stations. Metro managers are giving workers pamphlets that explain how to recognize a chemical attack.

Metro also is cracking down on its contractors, trying to account for extra equipment in its stations. "We've got to know whose toolboxes are whose, who's on the property at what time, making sure that gates are locked behind the contractors," Hanson said.

D.C. Police Chief Charles H. Ramsey and FBI officials will brief members of the Washington Board of Trade today on the significance of the Code Orange Alert. Residents in 14 Northern Virginia jurisdictions, including Fairfax, Arlington, Loudoun and Prince William counties, will receive a 16-page emergency preparedness pamphlet this weekend, officials in those counties said.

Security was heightened yesterday at the U.S. District Courthouse in Washington. Everyone entering the building at 333 Constitution Ave. had to show photo identification, and extra patrols were added around the building's perimeter, according to an internal memo from Circuit Court executive Jill C. Sayenga. There was no specific threat to the courthouse, officials said.

"I think security is enhanced in everything we do right now, in all federal buildings and across town," said Assistant Chief Deputy U.S. Marshal Pat Monardo.

Employees at the nearby U.S. Capitol pondered again what it meant to work inside a possible terrorist target.

"I'm very nervous, very concerned," said Letitia Bowens, 40, a District resident who is a cook in the Capitol cafeteria. "My mom says to be alert all the time and to keep my coat and pocketbook close by in case I have to evacuate."

But Dan Kidder, 31, of Springfield, press secretary for Rep. Mac Collins (R-Ga.), said he feels safer on the Hill than elsewhere in the District.

"The police officers do a fantastic job," Kidder said. He said he has been prepared for general emergencies since the millennium and that his office in the Longworth Building, like others, has "escape hoods" to give employees temporary smoke and biochemical protection if they have to flee.

In Virginia, former lieutenant governor John H. Hager Jr., who heads the state's office of commonwealth preparedness, urged people to take the government's recent warnings seriously but said people should not feel compelled to drop everything and run to the store.

"People can do it in due course," Hager said yesterday. "You should consider, when you next go, what your supply situation is at home."

Hager said he suspects that the warning was intended, as much as anything, to get people thinking.

"I think it's being used as a way to get people's attention, to say, 'This is a serious situation,' " Hager said. "We have a war here on our own turf. There was quite a blase{acute} attitude about warnings and about how this situation might impact me as a person, as opposed to the country."

Staff writers Karlyn Barker, Timothy Dwyer, Nelson Hernandez, Fredrick Kunkle, Lyndsey Layton, Arthur Santana, Ian Shapira, Michael D. Shear and Neely Tucker contributed to this report.

Chuck Pucie of Bethesda talks to Retta Nowlin and Alice Burr, both of Chevy Chase, at Strosniders Hardware, where they were buying supplies. At the Home Depot in Gaithersburg, Michelle Frank of Bethesda used a list from yesterday's Washington Post to shop, top.Rosemary Sump of Chevy Chase checks out at Strosniders Hardware in Silver Spring.