COLUMN ONE : Threats of Terrorism: When to Tell Public : The Unabomber’s targeting of LAX has sparked a high-profile alert. More often, authorities keep warnings under wraps.

When the notorious Unabomber told a San Francisco newspaper that he would blow up an airliner flying out of Los Angeles International Airport last week, the public was given a rare opportunity to personally assess a terrorist threat.

On hundreds of occasions every year, airliners, courthouses, subways and assorted public places are the targets of threats, and people are almost never told. That’s because most threats are either incredible on their face or easily invalidated, government officials and terrorism experts say. A little ignorance has gone a long way in insulating the public from needless anxiety, they contend.

But a decade of international terrorism, marked by two deadly airliner attacks in which travelers were not apprised of known dangers, has increased the legal and ethical demands for disclosure of such threats. More recently, the bombings of the World Trade Center in New York and the federal building in Oklahoma City have intensified the pressure on authorities who must decide what the public should know.

Airline passenger groups are advocating the right of travelers to make their own informed decisions about when it is safe to fly. “We, as airline passengers, are consumers of this product. The more information we have the better we can make those decisions about where and when we should fly,” said David S. Stempler, executive director of the Dallas-based International Airline Passengers Assn.

But many authorities say the maxim “better safe than sorry”--often cited in favor of public notification--is dangerously simplistic.

It fails to recognize the welter of conflicting goals that must be weighed in deciding whether to publicize a threat. Full disclosure can reduce risk but also foment public anxiety; it can reduce the possibility of lawsuits but also hurt business; it can encourage a public dialogue that can help law enforcement catch a suspect or it can inspire copycat crimes.

“After the World Trade Center bombing, there were 70 bomb threats a day [in New York City],” said Brian Jenkins, a consultant and terrorism expert. “At some point it becomes meaningless to keep warning people, and that can be just as dangerous as the threat being ignored.”

In recent years, particularly since a terrorist bomb downed Pan Am Flight 103 over Lockerbie, Scotland, in 1988, the airline industry has been forced to confront the question of when and how to issue warnings. Still, warnings are the exception both in that industry and in others.

Officials decided, for example, that visitors to Disneyland over the Easter weekend would not be told that the theme park had received a threat of a chemical attack. (The threat, coming on the heels of the deadly gas attack on the Tokyo subway, was serious enough that authorities summoned health officials and a chemical warfare team, before the FBI determined it was a hoax.)

Operators of the Criminal Courts Building in Los Angeles, in contrast, have usually opted to evacuate the building during a series of bomb threats coinciding with the O.J. Simpson murder trial. And the U.S. State Department has pursued an intermediate course--decreasing the number of admonitions against overseas travel, while increasing an information program that gives travelers more discretion to decide where it’s safe to go.

The decision about whether to publicize the Unabomber’s threat--to “blow up an airliner out of Los Angeles International Airport”--was made by the managers of the San Francisco Chronicle after they consulted with the FBI. The newspaper decided it would “do more good than harm” to write about the serial bomber’s one-paragraph missive, said Executive Editor Matthew F. Wilson.

Even if the media hadn’t received first word of the threat from the Unabomber, the decision to go public would have been “an easy call,” said the Federal Aviation Administration’s top security official. “You have a really credible threat that is from a specific source that has done bombings before,” said Cathal Flynn, FAA associate administrator for civil aviation security. “You are putting a lot of security measures into effect and you want the public to know and to cooperate.”

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It’s rare that authorities are presented with such a plausible threat, and feel so convinced of the need to engage the public in thwarting it. Still, the FAA did not feel compelled to invoke the highest level of warning--which requires notifying the public when flying may be unsafe because of a terrorist threat. The Aviation Security Improvement Act of 1990 followed the Pan Am bombing, which killed 270. It was learned shortly after the crash that travelers had not been informed that terrorists had threatened Pan Am flights, like the doomed one, which originated in Frankfurt, Germany.

FAA officials have ruled that hundreds of threats since Flight 103 were either bogus or adequately countered by precautions so that the 1990 law has never been invoked.

“The law requires you notify the public and sort of say, ‘You are flying at your own risk,’ ” said Flynn. “But that is not what we are doing here [in the Unabomber case] because we believe the heightened security meets the threat.”

A law stemming from an earlier airline tragedy also requires greater public disclosure of danger, but it has seldom been put in force. That law grew out of the June, 1985, murder of Robert D. Stethem, a U.S. Navy steelworker and diver.

Reports revealed that the hijackers who killed Stethem and held 153 passengers and crew hostage had boarded the jet in Athens, but that the airport’s slipshod safety measures had not been revealed to American travelers. Now the U.S. Department of Transportation is required to assess the safety of foreign airports and to publish a notice when they don’t meet safety standards.

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In the last decade, international airports in four cities have been the target of the warnings--Lima, Buenos Aires, Manila and, currently, Lagos, Nigeria.

Still, most threats never reach airlines passengers, even when they are made against specific carriers or flights. There have been 300 to 400 threats against planes a year in recent times, but with only a handful each year judged credible enough that searches were required, said a high-ranking FAA official.

Regulators leave it to the airlines to sweep for explosives themselves, sometimes with help from authorities, and to decide how much the public should know, say, about a plane that has been checked and put back in service.

Airlines representatives were reluctant to talk about such cases, but one executive said passengers are “in some instances told it’s an ‘operational’ reason, so we won’t panic them for no reason.” The executive, who requested anonymity, said his company also “tries to keep it as quiet as possible about something like that, otherwise copycats would come out of the woodwork. That is a big concern.”

Airline passengers’ advocate Stempler said travelers should be told more.

“They are telling us about these threats only when it rises to the level of a Unabomber or the threat this year in Asia [from a terrorist group operating in the Philippines.] Then they tell us,” Stempler said. “But we are not hearing enough. And we have no way of knowing what they aren’t telling us.

“The general security approach has been paternalistic,” he added. “ ‘We will decide for you whether it is safe or not to fly.’ But our ideas of what is safe or unsafe may be vastly different and I may have many other good options of how to travel.”

Travelers are most likely to hear about generalized threats to certain regions, rather than terrorist targets on a single plane. This February, the public was notified of increased security aboard jets in Asia because of bombing threats. Only last month did U.S. authorities reveal the specifics behind the threat--that the mastermind behind the New York World Trade Center bombing had been plotting to bomb 11 U.S. airliners flying over the Pacific Ocean in a single day.

Officials in a variety of settings declined to reveal the techniques they use to analyze threats, procedures that are often detailed in multivolume safety manuals. But personnel who field such warnings often are tipped off by the mundane.

In the case of the April threat against Disneyland, officials suspected a hoax, in part, because a letter and videotape threatened that “guests” would die--a term for patrons that is used by Disneyland employees. (The source of the threat has never been determined and Disneyland declined to comment for this story.)

An LAX employee who has fielded threatening calls said the object is to keep the caller on the phone long enough to give away their true motive. “Sometimes you can tell they are just drunk, or it’s a high school prank or they are someone who works at the airport--there are 100,000 employee out here--and is just disillusioned,” said the employee, who declined to be named.

While consumers might agitate for more information, the State Department concluded in 1992 that warnings about overseas travel were excessive and nebulous. Host nations complained that they frequently were the butt of safety admonitions even when they were statistically safer than many big U.S. cities. The designations could devastate tourism.

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As a result, the State Department dumped its longstanding designations of travel “notices,” “cautions” and “warnings.” It continues to issue warnings in the most severe cases, but more often simply publishes information bulletins with a less judgmental description of local conditions. “We try to leave it to the traveler to make their own informed decision about whether to visit a country,” said Nyda Budig, a spokeswoman for the State Department’s consular affairs section.

The potential danger of precipitous government action becomes most evident in a crowd. That’s why operators of the Los Angeles Memorial Coliseum chose not to tell the public about bomb threats that came in during two events about a decade ago. “An announcement could possibly engender a panic,” said a staff member who asked not to be identified. “More people could be injured that way, trying to get out, than by the bomb.”

Transit officials in New York City said they tend to close subway stations when threats are supported by the finding of suspicious packages, but they worry about the dangerous alternative that some edgy New Yorkers will select.

“In some areas you might have trains trapped between stations and it’s getting particularly hot and the air conditioning shuts down,” said O’Leary. “In a case like that, New Yorkers are likely to say, ‘Hey, I’m walking outta here.’ The problem if you overreact is that can create an even greater threat.”

The 15 bomb threats phoned in to the Los Angeles Criminal Courts Building since the start of the year have triggered 10 evacuations of some sections of the 18-floor building, enough that some employees report they are “numb” to the potential danger. Such a reaction can become particularly dangerous if it desensitizes security personnel who are charged with detecting explosives, said terrorism expert Jenkins.

But there are advantages to public notification. British officials were particularly dependent on their citizens, for instance, to help spot bombs in a transportation system that was deluged with threats up until a cease-fire last fall with the Irish Republican Army. In the year before the agreement, transportation police received reports of 1,415 suspect packages, many from a wary public.

Officials in London credit a public awareness campaign with helping to defuse the IRA threat. But Thomas Clarke, a Labor member of Parliament, conceded: “There is a thin line between preventing panic and avoiding disaster.”

With the public aware of the Unabomber threat, they could be informed of specific areas of vulnerability--such as strangers handing off packages to them for “delivery”--that authorities could not have countered on their own.

Some aviation officials say they feel compelled to disclose threats because of the Lockerbie disaster and ensuing litigation. In just two judgments following that case, juries awarded nearly $40 million for Pan Am and co-defendants’ purported failure to take proper precautions.

When U.S. Transportation Secretary Federico Pena flew to Los Angeles shortly after the Unabomber threat, he said he was demonstrating his confidence in the airport’s safety. But he added that the final decision on whether to fly was in the hands of travelers.

Stempler lauded Pena for not giving ironclad assurances.

One FAA official, who asked not to be named, thought he heard echoes of the Pan Am disaster in Pena’s comments. “No one here is going to talk in absolutes anymore,” said the official. “If they did, in the unlikely event something went wrong, some family is going to sue the secretary of transportation and everybody else, saying ‘But, hey, you said it was safe!’ ”

Times staff writers Kenneth Reich, William Tuohy and Jeff Leeds contributed to this report. Tuohy reported from London.