From airports to cattle feedlots to nuclear plants, the government has begun tightening security to fortify America against terror.

The plan, called "Operation Liberty Shield," goes far beyond the government's previous responses to threats of terror because officials believe war with Iraq increases the possibility of attacks on U.S. soil or against U.S. interests abroad.

It envisions close cooperation among federal, state and local governments, as well as private businesses such as chemical plants and banks.

Homeland Security Secretary Tom Ridge said individual Americans could play a part as well by staying vigilant and prepared while avoiding panic.

"There is bound to be misinformation. Don't react to rumors. We will strive to get the facts out there as fast as we can," Ridge said Tuesday.

The nation's terror alert status was raised from "elevated" to "high" Monday night after President Bush said the U.S. military was ready to attack Iraq unless Saddam Hussein and his sons left the country by Wednesday night U.S. time.

Intelligence and law enforcement officials believe the Al Qaeda terror network, while weakened, and its sympathizers remain the primary threat to mount terror attacks against America. There also is uneasiness about Iraqi agents or surrogate groups, as well as individual extremists or others.

Part of the homeland security plan requires that anyone seeking political asylum in the United States from 33 countries with known terrorism presences, including Iraq, be detained while the government considers claims they face political persecution at home.

Last year, 577 people from those countries — including 348 from Iraq — claimed asylum out of more than 58,000 who sought entry in the United States, according to immigration officials. The goal of detention is to prevent terrorists or spies from using America's willingness to accept refugees as a pretext for entering the country.

"We want to make absolutely certain, during this period of time, that you are who you say you are," Ridge said.

Much of the plan is geared toward protecting the nation's transportation system, including random searches of cars at airports, restricted airspace over certain cities, police or National Guardsmen protecting railroad bridges, enhanced identification checks for truckers who haul hazardous materials and more Coast Guard escorts of ferries and cruise ships.

The Coast Guard also is providing greater protection for petroleum and chemical plants near large cities. The General Accounting Office, which is the investigative arm of Congress, said in a report Tuesday that some of these 15,000 plants "may be attractive targets for terrorists intent on causing massive damage."

The report noted that nine months ago, Bush administration officials agreed on the need for mandatory security plans for such facilities, but no such plans have been proposed.

Security also is being increased at nuclear power plants, electric grids, subway systems and government buildings including the White House. In addition, the government is stepping up its tracking of the Internet for signs of terrorist activity and boosting security at financial markets, banks and other major parts of the economy.

Police in Washington turned on the city's network of 14 closed circuit cameras. The cameras monitor activity at key public places in the city, including the Mall, the White House, the Washington Monument, the Capitol and Union Station.

Monitoring of the food supply also is being enhanced, including more inspections of imported food and Agriculture Department action to encourage greater scrutiny of feedlots, stockyards and storage areas.

A separate GAO report issued Tuesday found possible gaps in food supply security because guidelines for the industry are voluntary, not enforced or monitored by the Agriculture Department or the Food and Drug Administration.

"Neither agency believes it has the authority to regulate all aspects of security at food processing facilities," the GAO said.

The Health and Human Services Department has a corps of doctors, nurses and other staff on alert in case of disease outbreak and is urging state and local officials to report any unusual diseases or disease patterns.

Meanwhile, the FBI and other police agencies are implementing a broad anti-terrorism plan that includes diverting thousands of FBI agents away from regular duties to focus solely on the terror threat. FBI-led joint terrorism task forces will be manned 24 hours a day, seven days a week during any war and perhaps longer.

That plan includes monitoring of individuals linked to terrorism, FBI interviews with thousands of Iraqis and others in this country and continued investigation of the financial apparatus used by terror networks to pay for their activities.