COLUMN ONE : Illusion of Immunity Is Shattered : America’s vulnerability to terrorism is brought home by the Oklahoma City bombing. Only luck and good intelligence work have sustained the nation’s fragile myth of security, experts say.

The World Trade Center. And now Oklahoma City.

Grim reality has been crowding steadily closer.

The age of innocence is ending as Americans realize that terrorism is no longer something threatening other people in other countries.

In fact, say federal officials and independent experts, it was an illusion from the beginning. A combination of luck, good intelligence work and efficient law enforcement have prevented scores of attempts at terrorist acts over the last 25 years, according to the FBI.

“International terrorism” first entered the modern lexicon three decades ago as leftist guerrilla movements clashed with rightist regimes in Latin America. From there, it spread around the world--most notably to the Middle East, where car bombs, like the one believed to have shattered the federal office building in Oklahoma City, are now part of everyday life.

But if America had remained relatively unscathed until the 1993 bombing of the World Trade Center in New York City, any hope of continuing immunity ended once and for all Wednesday.

The hulking concrete and steel shreds of the Alfred P. Murrah Federal Building drove the point home even more forcefully than the trade center bombing because of the very ordinariness of the target.

Hitting in America’s heartland--instead of a big, urban financial center--illustrates the vulnerability of virtually everyone. There is at least one almost identical--and identically vulnerable--federal office center in each of the 50 states.

“This shakes the fundamental faith people have in their security across this country,” said Dave McCurdy, a former Oklahoma congressman who served on the House Intelligence Committee.

From day-care centers in Dayton, Ohio, to shopping malls in Seattle, cities and citizens are likely to feel more exposed and more vulnerable. And rightly so, experts say.

“Welcome to the 21st Century. Terrorist attacks in the United States are only going to get worse,” said Bruce Hoffman, a former terrorism specialist at the RAND think tank in Santa Monica who now works at St. Andrews University in Scotland.

“The World Trade Center should have been a wake-up call, but it was instead widely seen as the act of amateurs and not a continuing threat. Because it worked in sowing terror, it was certain to happen again. This bombing takes that process one step further.”

To keep the threat in perspective, most experts do not expect that the United States will experience the relentless waves of terrorist attacks that shattered Lebanon and are sweeping over such countries as Algeria.

“We’re not on the front lines of a wave of mass terrorism in the United States,” said L. Paul Bremer, former head of the State Department’s Counterterrorism Office and now a consultant at Kissinger & Associates.

“We’re vulnerable, yes, but we have to be realistic. While we can’t protect every federal building in this country, from now on we’ll all be more careful.”

What could worsen the social and political impact of terrorism in the United States is the difficulty that both the government and the public will have in taking effective steps to prevent or limit future attacks.

Open borders, the sheer size of the country, the difficulty in monitoring illegal immigrants, the right and necessity of individual access to government facilities and a host of other factors integral to American life hamper the ability to control or seriously limit the threat, experts said.

“We’re very good investigators. We will be able to put together the fragments of that bomb and figure out what it was and the method of making it and who has that method. But we’ll have a problem in a free country preventing these attacks,” said Victoria Toensing, former deputy assistant attorney general for counterterrorism.

“Democracies are by far the most vulnerable to terrorism, because freedoms are used by terrorists to victimize us. Police don’t have the right and shouldn’t have for sweeps and searches,” added Oliver B. Revell, a former top FBI official in charge of anti-terrorism and now a private security consultant.

The difficulties Americans will face were foreshadowed in London during the 1990-91 Persian Gulf crisis. Unprecedented security measures were taken there to thwart terrorist attacks that officials feared might be launched by Iraq, especially against the prime minister’s residence and other key government buildings.

Yet despite these measures, a cell of the Irish Republican Army managed to get to within a block of the prime minister’s historic home and fire a mortar at it as the British Cabinet was meeting. The shell missed the building and landed in the back garden.

At other times, to prevent IRA attacks, sides streets throughout London’s financial center were closed off and main arteries were tightly monitored by police officers and remote-controlled video cameras.

“Those tactics may have some impact in a country with one major city but you can’t hermetically seal off any city from terrorist attacks,” Hoffman said. “And that’s really unrealistic in a country like the United States with dozens of major cities.”

Ironically, the Oklahoma City attack comes after major inroads in dealing with terrorism.

In 1994, there was not a single act of terrorism by either domestic or foreign groups in the United States. And international terrorism in 1994 was at a 23-year low.

In its annual report to be released next week, the State Department Counterterrorism Office shows that attacks against American targets overseas were more than halved. In 1992, according to the report, 142 incidents were recorded. In 1994, there were 66.

But numbers can be deceiving.

“These statistics are not a reliable index of the threat,’ Philip C. Wilcox Jr., State Department coordinator for counterterrorism, said in congressional testimony this month.

“Terrorists have expanded their global reach and today all nations and continents are vulnerable. Moreover, as governments have improved security for their officials and installations, terrorists are striking more frequently at soft, unprotected civilian targets.”

And in a hauntingly prescient addendum, Wilcox noted that terrorists are increasingly aiming at mass civilian casualties to increase the fear and disruption that they hope to inflict--and in the process “far overshadowing” the decline in numbers of non-lethal incidents.

U.S. information, transportation, medical and financial infrastructures are increasingly vulnerable to disruption by terrorists, both foreign and domestic.

Terrorism instigated by cult groups--such as Japan’s Aum Supreme Truth, which is suspected of involvement in last month’s chemical weapons attack in the Tokyo subway system--is a “pathological phenomenon” even more difficult to anticipate, diagnose and guard against, he said.

The Tokyo attack, and another in Yokohama this week, also point to the difficulties presented by high-tech and other non-conventional threats including nerve gases and biological weapons.

Almost certainly, the Oklahoma City bombing will provoke calls for tougher anti-terrorism measures.

For one thing, said former FBI official Revell, “the best you can do (now) is use magnetometers and X-ray packages. We’ve got to do something to give law enforcement the ability at least to collect intelligence on what these groups are doing and saying publicly. The way the law is today, this is something news reporters can do but federal agents cannot.”

Yet meaningful steps to bolster the government’s anti-terrorism arsenal, including stepped-up efforts by intelligence agencies to monitor individuals and groups inside the United States, are likely to collide with American freedoms.

As the FBI’s efforts to discredit Dr. Martin Luther King Jr. and other civil rights leaders during the heyday of former Director J. Edgar Hoover made clear, such powers have a history of turning into abuses.

Perhaps even more serious, the war on terrorism could change the fabric of American life.

“Most of us like to feel that we can protect ourselves in some way or other from danger,” said psychologist Dean Kilpatrick, director of the national crime victims research and treatment center in Charleston, S.C.

“Even though the fear of crime is something that is very prevalent among Americans, this particular type--no motive, you’re minding your own business, in someplace you think should be safe--and all of a sudden, many lives are snuffed out with no way to protect yourself. That’s going to have a profound influence on a lot of people.”

Others predicted that the death of so many young children in the federal building’s day-care center would raise feelings of guilt and fear among working parents, many of whom already struggle with such emotions.

“Working mothers who are generally conflicted about putting their children in day care to pursue careers find this kind of phenomenon exacerbates all those conflicts and guilt feelings,”’ said Rona Fields, an Alexandria, Va., psychologist and sociologist.

Yet terrorism specialists also argue that the Oklahoma City bombing is unlikely to be a catalyst for sweeping change.

“What are we going to do? Stop going to work?” said Noel Koch, former Pentagon official in charge of counterterrorism.

“The Europeans have lived with it for years. We’ll learn to do it too.”

Times staff writer Marlene Cimons contributed to this story.