COLUMN ONE : Illusion of Immunity Is Shattered : America’s vulnerability to terrorism is chillingly realized in the Oklahoma City bombing. Only luck, and good intelligence, have sustained the fragile national myth of security.

In April, 1988, a New Jersey state trooper noticed a vintage Mazda being driven at suspiciously slow speed. He pulled it over. The driver was carrying $3,600 in cash and a Swiss bank account card. On the back seat, in plain sight, were three steel canisters packed with gunpowder and attached to wires.

Dumb luck had interrupted what could have become the biggest act of international terrorism attempted up to that time in the United States. The man behind the wheel of the Mazda turned out to be Japanese Red Army terrorist Yu Kikumura. He was on his way to New York City to plant explosives on Wall Street.

“International terrorism,” a tragic phrase that first edged into the modern lexicon about three decades ago, began in Latin America in the late 1960s as leftist guerrilla movements clashed with rightists. 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 on Wednesday have become part of everyday life.

But the widespread American notion that terrorism is something that threatens someone else in some other country has been an illusion from the beginning, according to federal officials and independent experts--and an increasingly fragile one at that.

Grim reality has been crowding steadily closer. A combination of luck, good intelligence and efficient law enforcement has prevented scores of attempts at terrorist acts over the past 25 years, the FBI said.

And the illusion of U.S. 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 1993 bombing of the World Trade Center in New York, experts agree, because of the very ordinariness of the target.

Hitting the soft underbelly of the heartland--instead of a government landmark in Washington or financial symbols of the American way in New York City--brings home the vulnerability of every American everywhere. There is an almost identical--and identically vulnerable--federal office center in almost every city in the land.

“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 contended. Neither the Oklahoma blast nor the World Trade Center bombing was a fluke.

“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 Corp. 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,” he said.

What could make the social and political impact of terrorism inside the United States even worse is the difficulty both government authorities and the public are certain to have in taking effective steps to prevent or limit future attacks.

Open U.S. borders, the continent-spanning size of the country, the difficulty in monitoring illegal aliens, the right and necessity of individual access to government facilities and a host of other factors integral to American life will make it difficult 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 anti-terrorism official who now runs a private security consulting firm.

The difficulties that 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 at 10 Downing St. and other key government buildings nearby.

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

At other times, to prevent IRA attacks, side streets throughout London’s financial center, known as The City, 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. And that’s really unrealistic in a country like the United States with dozens of major cities,” Hoffman said.

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 now 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 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.”

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 says 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 attacks in the Tokyo subway system--is a “pathological phenomenon” even more difficult to anticipate, diagnose and guard against, he said.

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 traditional American freedoms.

As the FBI’s efforts to discredit Dr. Martin Luther King Jr. and other civil rights leaders during the heyday of 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 in subtle ways.

“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 at a day-care center would raise feelings of guilt and fear among working mothers who already are struggling to keep these emotions under control.

“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 who has studied terrorism.

Yet terrorism specialists also argue that, in the end, 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.

Times staff writer Marlene Cimons contributed to this story.