Security on Higher Alert Across U.S.

Although the Department of Homeland Security has not issued an alert, the agency remains at what the homeland security secretary, Janet Napolitano, has called a “heightened state of vigilance.” The State Department, on the other hand, has issued a worldwide travel alert to Americans.

In Philadelphia, the police commissioner, Charles H. Ramsey, has placed the department on “high alert,” increased patrols around religious buildings, and intensified security at tourist attractions and shopping malls, the police said.

“We haven’t added more personnel; we’re just doing more checks and asking our officers and citizens to be more aware,” said Lt. Ray Evers, a police spokesman.

The additional security includes hourly checks at some of the city’s synagogues and mosques, as well as arranging meetings with building superintendents and representatives of large businesses and manufacturers to remind them to report suspicious activity to the police, Lieutenant Evers said.

In Phoenix, officials said they had supplemented security at the city’s airport, municipal buildings and houses of worship and on its light rail system, said Scott Krushak, the coordinator for Phoenix’s Office of Emergency Management.

“We’re not doing it because we’ve had any threats, but because it is part of a ‘lean forward’ strategy we have here in the city of Phoenix,” Mr. Krushak said. “We are really relying on the community to tell us if they see anything.”

In Los Angeles, the police sent additional officers to the Staples Center for the Lakers playoff basketball game against Dallas on Monday, and officials said they intended to also supplement police patrols at Dodger Stadium. Even before the death of Bin Laden, security at Dodgers games had been stepped up after a fan of the rival San Francisco Giants was badly beaten in a stadium parking lot last month.

In addition, Lt. Andy Neiman, a police spokesman, said the police were paying particular attention to airports, ports and telecommunications hubs.

At Los Angeles International Airport on Tuesday, Debby Cummings, 44, who was on a flight from Detroit to visit friends in Los Angeles, said the security screening in Detroit seemed normal except that more passengers had been told to go through full-body scanners. Ms. Cummings said that she had not been overly concerned about flying, but that her 15-year-old son had worried the plane might explode.

“In Detroit they had two of the body scanners, which they were sending most people through, but other than that it was the same,” she said. “They only had one scanner before, and they didn’t used to make the majority of people go through it.”

In Chicago, the Police Department said it had sent additional officers to patrol around houses of worship, the Richard J. Daley Center, and at the United Center, where arena security personnel checked fans arriving to Monday night’s basketball game against Atlanta with handheld metal detectors.

Similar procedures were to be in place for an N.B.A. playoff game in Oklahoma City on Tuesday night and for all remaining basketball playoff games, officials said.

In Miami, the police have added officers with dogs at Miami International Airport, but many airports around the country, including those in San Francisco and Seattle, said they had taken no additional security precautions because the federal government had not issued a threat warning.

Timothy Williams reported from New York, and Ian Lovett from Los Angeles.