The communications raised concerns about hotels and subways in the city and the East Coast.
Law enforcement and private security stepped up scrutiny at the nation's borders, airports and hotels after the latest terror alert Friday, with worries raised about New York as a possible target.
Intercepted communications among suspected terrorists suggested a potential threat to New York, a high-ranking law enforcement source told The Associated Press.
The communications, some intercepted as late as Thursday night, raised specific concerns about hotels and subways in the city and the East Coast, said the source, who spoke on condition of anonymity.
The national alert spurred extra patrols on Minnesota's northern border, increased Coast Guard stops along both coasts, added more eyes at theme parks in Florida and California, and closed a southeast Kansas fishing lake beside the Wolf Creek nuclear power plant.
"It's not quite business as usual," said Colleen Dwyer, a Bureau of Reclamation spokeswoman at Hoover Dam on the Arizona-Nevada line, where more guards were assigned to the visitor center.
Private businesses snapped to attention along with law enforcement. "If Secretary [Tom] Ridge says there's a reason to be more alert, we will be," said Dick Turner, general manager of the Embassy Suites Hotel in Chicago.
Some in government and business would not discuss what steps they took, if any, after the nation's terror threat level went from yellow to orange, the second-highest in the color-coded warning system.
"We have not eased up on any of our security measures since 9/11," said Gerard Hoeppner at Tampa's Busch Gardens theme park. "The safety of our guests and employees is our highest priority."
Others said it was just one worry among many.
"The likelihood of an earthquake is more of a huge concern of mine," said Rob Huntley, general manager of The Inn At Union Square in San Francisco.
No targets mentioned
No specific targets were mentioned, though federal officials listed apartment buildings and hotels as potential targets along with facilities connected to transportation, energy and "symbols of American power."
As with past alerts, officials found themselves trying to warn people without panicking them.
"To be honest, going from yellow to orange for the average citizen means not much," said Massachusetts' Public Safety Secretary Ed Flynn. "Go on with your normal course of business."
Still, normal business could be thrown off as others in Flynn's state announced stepped-up patrols at Logan International Airport, on Boston's subways and in the waters off the Atlantic coast.
"What passengers may notice is increased state police patrols, more roadblocks and vehicle inspections," said Jose Juves, spokesman for the authority that runs the airport, where two of the planes in the Sept. 11 attacks were hijacked. "Passengers may see more frequent use of the bomb-sniffing dogs also."
Atlanta's hotels, arenas and bars were expected to be packed for Sunday's NBA All-Star Game and other events, but city, state and basketball officials said heightened security should ease any fears.
"We have already prepared at a high level. ... We've found no need to increase anything at this point," said Bernie Tolbert of NBA security.
At U.S. border crossings, inspectors began conducting more vehicle searches and running computer checks on all pedestrians, said Lauren Mack, an Immigration and Naturalization Service spokeswoman in San Diego. Before Friday, Mack said, inspectors ran computer checks on about 80 percent of pedestrians entering the country.
In New York, Gov. George Pataki said specialized units of the state police and the National Guard were activated. He and New York City Mayor Michael Bloomberg announced extra security at bridges, tunnels, airports, subways and many public buildings.
After the federal government alerted state governments to the change, a network of contacts quickly spread the word, urban to rural, government to business, and on to the public.