Top federal officials yesterday issued their most pointed advice since Sept. 11, 2001, on precautions the public should take against terrorist attacks, warning that every home should be stocked with three days' worth of water and food in case of a strike with chemical, biological or radiological weapons.

They also recommended that families consider designating a room where they will gather in the event of such an attack, and have on hand duct tape and heavy plastic sheeting to seal it, as well as scissors, a manual can opener, blankets, flashlights, radios and spare batteries. The officials said they believe the al Qaeda terrorist network is particularly targeting New York and Washington.

Ranking officials of the Department of Homeland Security told reporters at a briefing that Americans must take some responsibility for protecting themselves, but stressed that people should not feel panicked or abandoned by the government.

"We see information on citizen preparedness as prudent planning," said Gordon Johndroe, the department's spokesman.

But given al Qaeda's interest in weapons of mass destruction, he said, "It's appropriate for citizens to be informed about how to respond to a terrorist attack, much as people have prepared for years to be ready for tornadoes, hurricanes or floods."

While much of the information in yesterday's briefing was previously available on government Web sites, the news conference was an effort by federal officials to call attention to the steps individuals can take to prepare against the possibility of terror attacks.

"You have to talk to your family, and plan how you're going to communicate with each other" after a devastating terrorist attack, said David Paulison, the U.S. fire administrator, who is a top civil defense planner for the new department. For example, he said, families could designate a third party with whom telephone messages can be left.

The briefing came three days after officials raised the national terrorist threat index to indicate a "high risk" of attack by al Qaeda on U.S. targets here and abroad, and officials suggested privately that they do not want the gravity of the threat overlooked.

Department officials were offering what one acknowledged was "a complex message" with several elements to it. The first is that people must mentally rehearse for an attack, even though it is unsettling. Yet officials want citizens to remain calm and not view the situation as dire.

Law enforcement and homeland security officials have been criticized since soon after the Sept. 11 attacks for offering the public frightening but vague warnings while giving little guidance about what to do.

Homeland Security Secretary Tom Ridge and Attorney General John D. Ashcroft have often said Americans should "be vigilant," and on New Year's Eve people were advised to "avoid crowds."

Terrorism experts said that given large amounts of new intelligence, especially from Europe, suggesting that Americans could be targeted by weapons of mass destruction, U.S. government officials face the same public relations quandary they encountered in the past, but with higher stakes.

"While police departments and local governments have a menu of steps they take in reaction to the higher threat alerts, private citizens don't, and there's not a hell of a lot an ordinary citizen can do," said Brian Jenkins, a Rand Corp. specialist on counterterrorism. "That creates consternation, maybe even an atmosphere of terror that terrorists want to create. And so that leads the government now to try to offer advice to people."

"They're not trying to scare people, but to educate people," said Randall Larsen, director of the private Anser Institute for Homeland Security, who teaches security studies at the National War College. U.S. officials have studied the Israeli government's citizen preparedness campaign before the Persian Gulf War, when families were given gas masks and plastic sheeting to protect them from possible chemical attacks by Iraqi Scud missiles, he said.

"The Israelis learned one main task is psychologically preparing the population," Larsen said. "Americans need to be prepared the way the Israelis are. The most important message we could send to terrorists after the next attack is get up and go to work the next morning."

Paulison said one key message for the public is that, after a terrorist attack, people should listen to the news to learn what authorities are advising, and stay home if that is the recommendation. "If you don't have to evacuate, don't," he said. "The roads will be clogged."

But he laid out a vision of post-attack paralysis that made some other department officials wince. "People are going to be on their own for the first 24 or 48 hours," he said, reflecting on his experience with hurricanes as the former fire chief for Miami-Dade County.

Officials also offered details about actions the department has taken since Friday, when the threat level was raised from yellow to orange, the second-highest. Ridge, for example, held a conference call on Friday with 66 top corporate executives in charge of energy pipelines, utilities and other infrastructure to urge them to tighten security.

Department officials also contacted real estate management firms to urge them to impose new rules requiring visitors to tall buildings, as well as delivery workers, to obtain approval before entering. Likewise, mall owners were urged to begin moving parking for motorists, especially truck drivers, away from buildings. Many malls have hired armed guards in recent days.

Owners of all large buildings are being urged to secure air-intake equipment to prevent attempts to kill people with chemical weapons. Hotels have been told to restrict underground parking.

"The announcement on Friday was a signal to private industry and to state and local officials that more actions need to be taken," Johndroe said.

Officials are particularly concerned about intelligence that al Qaeda is targeting synagogues and other Jewish institutions. That has prompted a significant tightening of security at those places in recent days.

U.S. officials said one reason for yesterday's advice, and release of information about security discussions, was that al Qaeda tends to avoid targets it feels have been hardened.

"When we have more protections up, and signal we're paying attention, it lessens al Qaeda's interest in attack," an official said.

Staff writer Dan Eggen contributed to this report. Preparing for Terrorism Homeland security officials are recommending steps for households to prepare for a possible terrorist attack. * Assemble a disaster kit with essential food, water and supplies for three days. This should include one gallon of water per person per day, a first-aid kit, blankets and non-electric can openers. Also keep an emergency supply kit in your cars at work. * Keep on hand a radio with extra batteries to listen to broadcasts from local authorities. It may be safer to take shelter at home than to take to the roads. * Designate a room in your home where you can take shelter in case of a chemical or biological attack. Have on hand a roll of duct tape, scissors and plastic to cover doors, windows and vents in the room. * Talk with your family about potential emergencies and how you would respond, including what to do in an evacuation. * Plan how your household would stay in contact if separated. Identify two meeting places. * Pick a friend or relative out of the area for household members to call to say they are okay. * Post emergency numbers by the telephone.