WASHINGTON, March 17 — Fears of possible attacks in retaliation for U.S. military action in Iraq led the Homeland Security Department to raise the nation’s terror threat assessment Monday night to “orange,” the second highest of five levels, NBC News has learned. The new threat level went into effect after President Bush addressed the nation.

THE TERROR THREAT has been at “yellow,” the middle of the range, since last month, when it was raised for much of February because of concerns of a possible terrorist attack against U.S. interests overseas.

An official at the Homeland Security Department told NBC News that state officials were formally notified of the alert status in a conference call Monday night.

The official, along with others in the intelligence community, said there was specific intelligence that pointed to a desire by Osama bin Laden’s al-Qaida network to carry out attacks against the United States and U.S. interests.

In his address Monday night, Bush said he had ordered increased security at airports and along U.S. waterways.

Terrorist attacks “are not inevitable. They are, however, possible,” he said. “We will not be intimidated by thugs and killers.”

U.S. officials said there were no plans to raise the alert to the highest level, “red,” or to close national facilities unless something specific was discovered. But NBC News has learned that many major cities are taking the new warning more seriously than previous alerts, which have been criticized for being overly vague.

Under what officials code-named Operation Liberty Shield, New York planned to step up patrols around bridges, tunnels and subways, with specially trained antiterror police at hotels, apartment buildings, mosques and synagogues. Coast Guard and harbor police will aggressively step up water patrols, making more checks of incoming boats.

In Miami, there will be more security around the city’s big convention hotels and cruise ships. Police Chief John Timoney said the warning to be announced Monday night was of a different character from previous orange alerts.

“It’s almost like ‘orange plus,’ orange and a high a state of alert as far as what you see,” Timoney said. “But mentally, there is a clear understanding — ‘Hey, you know this is the real thing now.’”

Washington officials planned tighter security at prominent landmarks in the nation’s capital, as well as more helicopter patrols.

EVERYTHING WE CAN’

Los Angeles Mayor James Hahn acknowledged that, as has been the case in previous orange alerts, the nature of the threat was not specified. But like Timoney, he, too, said this one appeared different.

“Even though we’ve received no specific information that there’s any threat directed toward Los Angeles or the Southern California area, we continue to do everything we can, as prepared as we can,” he said.

Concerned about a potential attack from Iraqi sleeper cells, the FBI was sending agents fanning out to interview as many as 10,000 Iraqis now in the United States, urging them to report anything suspicious in the Arab community. FBI evidence specialists were to begin a 24-hour-a-day watch to analyze information U.S. troops found in Iraq.

“This war against Iraq may serve as a catalyst for a number of things, including terrorist actions in the U.S., suicide bombings, terrorist actions against the embassies around the world,” said James Bamford, a specialist on terrorism who has written widely about the National Security Agency.

By Pete Williams and Robert Windrem
NBC NEWS