The threat of retaliatory attacks from Middle East terrorists dropped a chill on Americans last week that forced the cancellation of overseas travel plans and prompted many to rethink the safety of attending public events at home.
Time and time again, the United States has heard the angry threats of retribution. Yet, relatively few have hardened into reality.
In December 1981, for example, the nation was set on its ear when reports surfaced that Libyan President Muammar el Kadafi had dispatched hit squads to assassinate President Reagan. While security precautions were markedly stepped up, the hit men never materialized.
But now, with the United States leading the charge against Iraqi President Saddam Hussein, Americans at home and abroad are being bombarded with yet another round of warnings as the government beefs up security worldwide.
They are cautions, terrorism experts agree, that are quite warranted, particularly overseas.
But this time, the anxiety and apprehension over a possible attack within the borders of the United States seem higher than before. There are concerns about terrorist acts against crowds at sporting events and shopping malls, against municipal water supplies and office air-conditioning systems.
"There's a line between prudence and paranoia," said Bruce Hoffman, an international terrorism expert with the Rand Corp. in Los Angeles.
"It's certainly prudent to increase security at potential terrorist targets, certainly prudent to address vulnerabilities," he said. "In essence, we have to do that, lest we send the wrong message to terrorists and invite them or embolden them to undertake an attack because they think we've left it undefended or left it vulnerable.
"But at the same time, that doesn't mean we should become paranoic that there's an actual, immediate, monolithic terrorist threat in this country right now."
The FBI, which is charged with detecting and deterring terrorist acts at home, considers the risk of attack "extremely high worldwide" and is taking the threats "extremely seriously," a spokesman said last week.
But FBI officials tempered their concern for attacks here at home.
"The level is lower right here in the U.S. than it is overseas," said Special Agent Thomas F. Jones, FBI spokesman in Washington.
Yet by no means, did he rule out the possibility of an attack.
"I don't think we could prevent a terrorist incident in this country," Mr. Jones said. "We have a lot of borders in this country, and to think that we could cover every inch of it would be very naive."
The FBI, bolstered by information from Western intelligence agencies, feels satisfied that agents probably would hear of organized plans by a specific group, he said.
"Our main concern would be with the individual zealot who, for whatever reason, would take it upon himself, or herself, to commit a terrorist act," Mr. Jones said. "That would be very hard to detect in advance."
It is just that prospect that has Mr. Hoffman concerned. "The bad news is that there's no way to predict what a lone terrorist might attack, but the good news is that he has far inferior capabilities, and generally his act of violence would be far less HTC consequential."
Dr. Robert H. Kupperman, a terrorism expert at the Center for Strategic and International Studies, acknowledged that there was less of a risk of a terrorist strike at home, but he did not discount it.
"In a war with Saddam Hussein, terrorism will be the weapon of horizontal escalation, of irregular warfare," Dr. Kupperman said. "It is certainly a tool for broadened warfare.
He said that Palestinian terrorist groups that have carried out attacks in the past have aligned themselves with Iraq and present the greatest threat.
In particular, he mentioned the Abu Nidal organization, which staged the December 1985 attacks on the Rome and Vienna airports that killed 19 people, and Abu Abbas, whose men attacked the cruise ship Achille Lauro in October 1985, killing Leon Klinghoffer, a vacationing U.S. citizen.
"They are presently in Baghdad, and they are known as very effective terrorists," he said. "Abu Abbas has threatened widespread terrorism, were we to attack Iraq."
But with the exception of the bombing of Pan Am Flight 103 -- which blew up in December 1988 over Lockerbie, Scotland, killing 259 passengers, 188 of whom were Americans -- very few U.S. citizens are killed overseas by terrorist acts State Department statistics show.
And fewer incidents occur in North America than the number of Americans killed abroad through acts of international terrorism. (See box.)
Yet those statistics offer a somewhat distorted view, given that about 25 percent of the international terrorist attacks each year target American citizens, property and companies -- a dubious honor shared with the Israelis, who also are targets of about 25 percent of such attacks, State Department figures show.
So far as domestic attacks, the FBI confirmed five non-international terrorist incidents in the United States during 1990, four of which were in Puerto Rico. The fifth involved a bomb exploding outside a Los Angeles building in which the IRS is housed, Mr. Jones said.
"Abroad, the threat [against Americans] now is quite high," Mr. Hoffman said, in unanimous agreement with other experts and U.S. officials. "Common sense dictates that in cases of increased international tension -- with a war going on -- the threat increases commensurately."
Terrorist attacks at home present much less of a risk, he said. "You have to put it into perspective," Mr. Hoffman said. "From 1980 to 1989, 4,077 people died from terrorist attacks. But 2,000 people a year are murdered in New York City.