Washington ? A deadly shooting attack at Los Angeles Airport breached the unprecedented security precautions imposed nationwide Thursday to protect American lives on the Fourth of July.

The military temporarily reactivated post-Sept. 11 combat jet patrols over Washington and New York. Other cities also got the overflights, although the Pentagon would not name them. And security zones were imposed at public places such as New York’s Empire State Building and the Gateway Arch in St. Louis.

The shooting at Los Angeles was characterized as likely “an isolated incident” not connected with terrorists.

There was unprecedented security on the National Mall where fewer people than usual were going to watch one of the country’s premier fireworks displays. Officials of Washington’s transit system said about a third fewer people were reported taking trains to the Mall than last year. Those who attended had their bags searched.

In Los Angeles, three people were killed at Israel’s El Al airlines ticket counter at the Tom Bradley International Terminal, including the gunman.

FBI agent Richard Garcia said that so far, it appeared to be an “isolated” incident. “We are just not aware of any other threat,” said Garcia.

California Gov. Gray Davis said extra law enforcement officials were on duty across the state. He urged people to report anything unusual, but otherwise to “go on with their celebration … This is America’s birthday.”

Airports beef up security

Airport officials in a number of major cities including Boston, Miami, Chicago and Philadelphia said that security at their airports was especially tight because of the holidays. But they said no additional actions had been taken because of the Los Angeles shooting.

New York City Police Commissioner Ray Kelly said authorities are beefing up security at El Al ticket counters in the New York area. Tight security was evident at the Empire State Building. Bomb-sniffing dogs patrolled the city’s transportation hubs.

“We’re using our bomb squad, our aviation units, our harbor patrol. The joint terrorist task force is deployed throughout the city,” said Kelly. “We believe we’re doing everything we reasonably can do to make this a safe holiday.”

In New York, the FAA announced temporary flight restrictions below 10,000 feet over virtually all of Manhattan from the Hudson River to the East River, from the Statue of Liberty to George Washington Bridge.

In St. Louis, a pleasure boater wandered into a restricted areas around the Gateway Arch. During a chase a water patrol boat and a U.S. Coast Guard vessel collided. No one injured. The boater had entered the restricted zone by mistake and was not cited.

The FBI said a group with terrorist ties had downloaded images of two U.S. stadiums Edward Jones Dome, home to the NFL’s St. Louis Rams, and Indianapolis’ RCA Dome from the Internet. Both stadiums were closed for the holiday.

Security centers busy

The new round-the-clock Homeland Security Coordination Center was monitoring nearly 2,100 medium and large Independence Day events nationwide.

The command center in Washington, with open lines to each of the celebrations, is staffed by special liaisons from the FBI, Secret Service, Federal Emergency Management Agency and Department of Health and Human Services.

A Homeland Security spokesman said the agency was using the July Fourth monitoring as a model for future preventative action. “Coordination is going fine,” Gordon Johndroe said. “Once these events are over, we’ll keep going strong.”

Visitors to the National Mall opened coolers and picnic baskets for inspection by police armed with hand-held metal detectors at 24 security checkpoints along a double line of snow fencing. More than 2,000 police, some from as far away as New Jersey were on duty.

“The visual presence gives people a feeling of safety,” said Dennis Southwick of Seattle. Others said that the tight security and concern about terrorism probably kept some people away.

Still, some visitors came, in part, because of all the talk about terrorism.

“We just wanted to make a statement that we’re here,” said Rhonni Greig of Ventura, Calif. She and her husband, Bill, dressed each of their three children 7, 10 and 12 in T-shirts featuring one of the three colors of the flag.

Floretta Calhoun, a member of Indianapolis’ Circle City Cloggers, said her worries disappeared once she arrived. “I had a little apprehension, but I thought, you can’t build your life around something like that,” said Calhoun, 78.

Police patrolled smaller parks along the Potomac River, where thousands planned to watch the fireworks.

Plainclothes FBI agents were walking Fourth of July parade routes in an all-hands response to heightened communications traffic between terrorist operatives overseas, although there was no specific threat against a target in the United States. Some U.S. embassies overseas canceled July Fourth celebrations.

President Bush planned to host an invited crowd at the White House after spending the morning with veterans in the courthouse square of Ripley, W.Va.

“Throughout America, local law enforcement agencies are exercising their discretion about how to beef up, step up preventive measures,” said White House spokesman Ari Fleischer. “It’s visible for all to see.”