Federal officials had a message for Americans on Monday, one day after the nation's terror alert was raised to "high": Just go about your business.

Homeland Security Secretary Tom Ridge (search) met with President Bush and other members of the Homeland Security Council to discuss the nation's jump to "Code Orange," or "high" status, from "Code Yellow," or "elevated" status.

Ridge told reporters that Americans should continue with their holiday travel plans and should do what they normally do because if they don't, then the terrorists will win.

"We cannot quit being Americans just because of these threats."

Bush advised people to "go about their lives."

"Our government is doing everything we can to protect our country," Bush said. "American citizens need to go about their lives, but as they do so, they need to know that governments at all levels are working as hard as we possibly can to protect the American citizens."

Earlier Monday, Ridge made the rounds of morning television news programs to calm a nation that may have been alarmed after the terror alert went up on Sunday and to urge Americans to be prepared.

"I think it's very, very important to send a message to the terrorists of goodwill and resolve," Ridge said.

White House Press Secretary Scott McClellan echoed Ridge's remarks during his news briefing Monday.

"Americans should go about living their lives, but they should remain vigilant," McClellan said. "Americans can take steps just like the government is taking steps to prevent an attack from happening in the first place. They can report suspicious packages, unattended briefcases or other unusual materials immediately to law enforcement authorities."

McClellan said Americans can "make a plan for what they and their family would do in an emergency" by following suggestions at the Homeland Security Department's Web site at http://www.ready.gov.

He also said, "the best away to prevent an attack from happening in the first place is to take the fight to the enemy and that's exactly what we have been doing since Sept. 11."

The move to a higher terror alert followed warnings that Usama bin Laden's terrorist network Al Qaeda (search) may be plotting attacks against the United States during the holidays.

"The information we have indicates that extremists abroad are anticipating near-term attacks that they believe will either rival or exceed" the Sept. 11, 2001 attacks, Ridge had said in announcing the upgraded alert status on Sunday.

Some of the intelligence information gathered indicates that Al Qaeda is seeking again to use planes as weapons, he said. Ridge said the terrorists are "constantly evaluating procedures ... to find gaps in our security posture that could be exploited."

The Transportation Security Administration (search) said Monday that the nation's airports have increased vehicle inspections, parking restrictions and bomb-sniffing canine patrols in response to the higher threat level.

Airport screeners are working overtime and their managers are helping staff security checkpoints, the agency said. "We're putting all hands on deck," spokesman Darrin Kayser said, adding that the TSA had already beefed up its staffing for the holiday travel rush.

Local law enforcement agencies are helping with airport security by patrolling terminals inside and out, as well as around runways. "Increased parking restrictions may require folks to park a little farther away than they might normally," Kayser said.

According to an advisory sent out Sunday by the FBI's Counterterrorism Division and the Department of Homeland Security and obtained by Fox News on Monday, reliable sources suggest the possibility of attacks against the United States by early 2004.

The six-page nationwide message sent to law enforcement and security personnel warns of the increase in threat activity and the change in the threat level from yellow to orange. The advisory also describes the methods for increasing security and also for identifying indicators of WMD threats.

The country's alert level had stood at yellow, an elevated risk and in the middle of the five-color scale, since May. On Monday, Ridge said the change in the alert status was the result of information from "many sources," but said he could not be more specific.

An official speaking on condition of anonymity had said Sunday that some of the intercepted communications and other intelligence mentioned New York, Washington and unspecified cities on the West Coast. Authorities are also concerned about dams, bridges, nuclear plants, chemical facilities and other public works.

Thousands of state and local law enforcement agencies have received an FBI advisory urging special notice of sites that could be targets and potential security upgrades, the official said.

A senior Pentagon official said Monday the Defense Department is helping beef up security, but declined to give details. In past times of high threat, officials have increased combat air patrols by military jets over U.S. cities and deployed missile launchers outside the Pentagon and at other locations in the capital.

Ridge said Sunday that credible intelligence sources "suggest the possibility of attacks against the homeland around the holiday season and beyond," and said the U.S. decided to raise the alert level after U.S. intelligence agencies "received a substantial increase in the volume of threat-related intelligence reports."

Hours after Ridge's announcement, the State Department issued a worldwide caution warning U.S. citizens overseas that they may be terrorist targets.

Ridge said officials did not see a connection between the recent capture of ousted Iraqi leader Saddam Hussein and the heightened security alert, and L. Paul Bremer (search), the U.S. administrator in Iraq, backed that up Monday, telling NBC he saw no connection.

"There's been a suggestion of high terror threats certainly in Iraq, where we are on the front of the war on terror over the last weeks, unrelated to Saddam's capture," Bremer said.

On Friday, the Arabic television network Al-Jazeera aired a new statement from Ayman al-Zawahri, bin Laden's chief deputy. The CIA said Saturday it believes the tape is authentic.

"We are still chasing the Americans and their allies everywhere, even in their homeland," according to the voice on the tape.

Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said earlier Sunday that officials were trying to determine whether the increased material detected was an aberration or something more serious.

"There is no doubt, from all the intelligence we pick up from Al Qaeda, that they want to do away with our way of life," he told "Fox News Sunday" after his return from a trip to Iraq and Afghanistan.

The threat level has been raised to orange four times before. Each change sets off a flurry of increased security measures by cities, states and businesses.

The lowest two levels, green and blue, and the highest, red, have not been used since the system was put in place in early 2002.

Fox News' Anna Stolley and The Associated Press contributed to this report.