WASHINGTON » When Stephen L. Holl, the chief of police at the Washington Metropolitan Airports Authority, gathered his staff for the regular morning meeting on Monday, he opened with a sobering assessment.

"It wasn’t our turn this time," said Holl, who oversees security at Reagan National and Dulles International airports. "Our turn could be next or it could be never."

"We believe this could happen any time," he later added.

The shooting last week at a security checkpoint at Los Angeles International Airport that left one Transportation Security Administration official dead and two others wounded has security experts re-examining strategy for making airports safe, but they say there are no obvious solutions and that extending any security perimeter raises other problems.

"Wherever you establish a security perimeter, by definition, there’s stuff outside it," said Arnold Barnett, an aviation security expert at Massachusetts Institute of Technology, explaining why it was hard to guard the people at the gate. Placing additional police officers outside the security perimeter, like at the ticketing area or at the curb, could simply prompt a gunman to go where the officers are not.

In a July 4, 2002, shooting at the Los Angeles airport, a man with a handgun waited until police officers left the area in front of the El Al Airlines ticket counter before he shot and killed two people and wounded several others. An El Al security guard shot and killed the gunman.

The chief of the Los Angeles Airport Police Department, Patrick Gannon, has defended his recent decision to reassign armed officers from the security screening area, saying it would allow them to patrol the airport more freely and avoid becoming too predictable. He said the biggest threats to terminals are from the curb areas to where passengers are screened and he wanted more officers available for those areas.

"We changed our strategy to a certain degree," Gannon said. "I can’t run the same thing every day." He said the redeployment had allowed officers to respond to the shooting within seconds and stop the gunman from harming more people.

While intelligence might stop terrorists, lone gunmen are much tougher to anticipate and stop, especially if they seem intent on suicide, as many believe was the case with the man suspected in the Los Angeles shooting, Paul Ciancia, who wrote a long note indicating he was targeting TSA officers. Gannon said Monday that Ciancia had entered wearing regular clothes and would not have raised suspicion from any officer who saw him.

As at many airports across the country, Los Angeles airport officials place officers at the curb, primarily to prevent car bombs. Setting up checkpoints at the traffic lanes leading to the airports, done in times of heightened tension, would not have helped in this case, experts say.

The police at the TSA checkpoints are there mostly to make sure passengers comply with the screeners and to arrest those found to be carrying guns.

Officials for the union that represents some 45,000 TSA agents have renewed their call to give at least some of its members a law enforcement status and allow them to carry guns.

"We’re not talking about arming and deputizing everyone, but we need to have a consistent and effective force to back up our officers," said David Borer, the general counsel for the American Federation of Government Employees. "Right now it’s left to local law enforcement and it’s a real patchwork. It worked this time, but I am not sure if we would have the same response in another airport."

Some safety specialists have long warned that creating crowds of people at the entrances to the airport gate areas merely moves the area of vulnerability from the planes to a more distant place — arguably safer, because gunfire at a security checkpoint would not make a plane crash.

Researchers are trying to create security systems that would avoid crowds at the checkpoints by allowing passengers to stroll through, putting their carry-ons on a fast-moving conveyor belt.

"All kinds of things could be happening — sniffing for explosives, X-rays, body scanners, or all of the above," said Vahid Motevalli, a member of a Transportation Research Board committee called "Checkpoints of the Future."

But that technology is probably quite distant, he said, and if a gunman specifically targeted TSA agents, even that futuristic checkpoint might not help.

Marshall McClain, the president of the airport police union said the number of officers at the airport had been cut for each of the last three years, making it more difficult to patrol the sprawling area.

"Part of our job is to be a deterrent and one way you’re a deterrent is by being seen," McClain said. "We need to be out there monitoring traffic and have a steady force at all times."

Motevalli, the associate dean for research and innovation at the Tennessee Tech University College of Engineering, said that the Los Angeles shooting was different from the terrorism that the existing security protocols were established to combat and had more in common with a workplace or school shooting in the way the victims were targeted.

Like others, Motevalli pointed out that such attacks predate the TSA and have continued. "It’s not politically or religiously motivated," he said. "It seems to be mental illness of some kind."

Some believe a strong police presence outside the airports’ "sterile area" could scare off attackers or at least end an attack more quickly. Paul Hudson, president of the passenger advocacy group FlyersRights.org, said that airport officials should follow the example of Grand Central Terminal in New York City.

"They have uniformed agents there with essentially Uzis, standing around," he said. Hudson said such a show of force at airports was in place after the attacks of Sept. 11, 2001, but was later withdrawn. An official at another airport, who asked not to be named, described such a show-of-force strategy as "scaring the gunman away so he goes to the mall instead."

Brian Michael Jenkins, a former Green Beret captain and a security expert at the RAND Corp., argued that increased security for crowded public places might not be worth the expense and challenge.

"If your only achievement is you’ve forced your shooter or terrorist bomber to drive three blocks further to another crowded place, that’s not really a net security benefit," he said. "If a person is denied access to a crowded airport, he can go to a train station, bus depot, a supermarket, or a theater, as we saw in Aurora, Colo., or a shopping mall, as we saw in Nairobi, or Times Square."