AVERTING TRAGEDY : HOWEVER COMFORTING IT MIGHT BE, INCREASED SECURITY WILL NOT BE ABLE TO DETECT ALL TYPES OF EXPLOSIVES. THE SPENDING SHOULD BE INSTEAD ON ADDED INTELLIGENCE GATHERING.

Byline: Joseph Finder

WHETHER or not the crash of TWA Flight 800 was caused by terrorists, Americans are calling for heightened airport security to ensure against another tragedy.

And on Thursday, President Clinton added to their demand by announcing new safety measures for airports. The tighter security includes more questioning of passengers in check-in lines and more inspections of carry-on baggage. Also, curbside baggage check-in will be eliminated on international flights.

While there's no question that security measures at airports must be enhanced, we are deluding ourselves if we think that is the way to prevent terrorist attacks.

Even the most sophisticated luggage scanners are enormously limited. This is not something airline or law-enforcement officials are comfortable talking about, particularly now, but the million-dollar machines we've been hearing so much about lately - the ones that have been installed in only three American airports - are still of limited value.

They may represent an improvement at detecting plastic explosives, but they're unlikely to be reliable at detecting certain other forms of explosives.

These machines, which use a combination of X-ray and CAT scan technology to generate three-dimensional images of what is inside bags, are programmed to locate substances that have the density of plastic explosives.

Yet many explosive materials, like foams or even liquid rocket propellants, have a lower density than plastic, are almost as powerful and can escape detection.

Terrorists will always figure out a way to defeat whatever security measures we put into place. They always have. What, then, can we do to prevent attacks?

Early warnings of terrorist plots can be provided by good intelligence, but here too there are great constraints. It's extremely difficult, sometimes impossible, to penetrate terrorist organizations.

Yet there is a role for our technical intelligence agencies, chiefly the National Security Agency and its British equivalent, the Government Communications Headquarters.They are quite skilled at intercepting communications - voice, data, faxes - around the world and combing them for certain ``trigger'' words in a designated string order.

But such intercepts rely on locating targets, which can only be done by human intelligence - ``humint,'' as it's called at Langley. To locate and recruit the people who are well placed takes money and patience, and it rarely shows results.

Thus, it is not surprising that in the last decade or so the CIA has cut back drastically on ``humint.'' But that is a mistake.

The FBI's counterterrorist abilities are impressive, but without the support of our foreign intelligence agencies they will remain ineffectual at preventing terrorist incidents.Both the CIA's and the Defense Intelligence Agency's counterterrorism abilities remain woefully undeveloped and a low priority.

In the CIA, for instance, counterterrorism is not an area where many are likely to make a career: the probability of success, after all, is low.

Intelligence insiders complain of being hampered by all manner of bureaucratic problems. ``We're awfully good at collecting data,'' they say, ``and even better at `briefing' it, but we're weak at putting it into a usable form.'' Analysts spend far too much time chasing data and not enough time analyzing it.

And there is a larger problem. As a people, we tend to react in fits and starts. We lurch from queasy isolationism to the gung-ho patriotism of the Persian Gulf War and back again.

What are terrorists, or would-be terrorists, to make of a nation that retaliates forcefully by bombing Iraq's intelligence headquarters after learning of a plot to assassinate former President Bush, yet hesitates to go after the Libyan bombers who brought down Pan Am Flight 103?

Ours is a culture of seat belts and air bags. We believe we have a natural right to a risk-free environment, and we're appalled when the fallacy of that belief is brought home. We've been astonishingly lucky.

Band-Aid measures such as the use of more and more sophisticated detection gadgetry may reassure a jittery public. But they're no substitute for facing the multipolar threats of a post-Cold War world head on.

MEMO: Joseph Finder, author of ``The Zero Hour,'' writes frequently on intelligence and international affairs.

CAPTION(S):

2 Photos

Photo: (1--Color) Moment of silence: A woman is comforte d while praying near the TWA crash site.

Associated Press

(2) Security check: New measures will include more inspections of carry-on baggage.

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