TERROR IN OKLAHOMA CITY : Experts See High Costs as Deterrent to Increased Bomb Detection Effort : Technology: Means exist to recognize explosive devices. But expense, annoyance to public transportation make identification difficult.

Just as global terrorists have learned to make bombs smaller and more deadly, the technology for recognizing explosive devices has been improved so much that experts can detect bombs across a room, concealed in envelopes or lining a briefcase.

But despite all their technical acumen, several bomb specialists said, the prohibitive cost of detection machines and the free flow of vehicular traffic make it virtually impossible to identify most bomb-carrying vehicles that might be driven to a federal building or a highly populated area.

“It’s possible to detect car bombs,” said Tony Fainberg, a senior associate at the Office of Technology Assessment in Washington. “But it would be too expensive and too cumbersome to be practical. We can protect some buildings but not all.”

Spurred by the 1983 truck bombing of the Marine barracks in Lebanon that claimed 241 lives and numerous other bombings in the last decade, a loose coalition of domestic and international law enforcement agencies, high-technology firms and businesses with global interests have sought ways to protect against terrorist attacks. Their work has yielded new products with the capability to “see” through walls, scan luggage in airports or detect vapors that reveal hidden explosives, according to experts familiar with the developing technology.

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Several officials in the federal government have formed an interagency terrorism support working group that has been meeting to encourage such projects for more than a decade. The group will conduct a seminar next month to review the latest in bomb detection technology, said Michael Kraft, a counterterrorism specialist at the State Department.

“There is a lot of energy being expended on research in this area,” said Kraft, noting that the federal government has budgeted about $8 million for such research.

Michael Johns, a retired structural engineer in Bethesda, Md., who has served as a safety and design consultant for governments and businesses, said that two options are available to protect buildings from bomb blasts. They can be made into fortresses or bomb detectors can be incorporated. For example, he said, buildings and city streets could have built-in laser sensors that scan passing vehicles or nuclear detectors that sense explosives inside car trunks or vans.

But fortress architecture and detection devices are both highly unpopular and too costly to be practical solutions, Johns said.

“There’s an awful lot that we can do,” he said. “We’ve thought about it a lot as a nation over the past 12 years or so. But this nation is beset by financial constraints . . . (and) the biggest problem is the patience of the public, which wouldn’t stand for such measures.

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“The question isn’t technical or whether we can do it. We can. Rather, will we find the will or the economic posture to do it? That’s the question.”

In some cases, the cost of ensuring safety has been embraced by the public, which views metal detectors and X-ray scans as an omnipresent annoyance at airports and entrances to government buildings.

But such measures are only effective for small bombs, guns and weapons and do little to protect against car bombs.

Ironically, a tiny bomb is more likely to be found by law enforcement officials because the most effective detection devices require a pass-through inspection, such as those used at airport gates.