COLUMN ONE : Decade of Digging Aids Iraq : Hussein imported state-of-the-art bunker-building techniques. Now much of his military punch--and the leader himself--may be protected.

A small French fishing net company was thrilled a decade ago to sell millions of dollars worth of its material to Iraq for use as military camouflage.

There was nothing wrong with the decision, company officials would lament later, because Iraq was then at war with the Western World’s personification of evil, Iran’s Ayatollah Ruhollah Khomeini.

The same reasoning made it easy for a Belgian construction company, along with a government-controlled Yugoslav firm, to build hundreds of underground bunkers across Iraq.

And a British nonprofit company that had been established to teach people how to construct bomb shelters provided Iraq with detailed plans for large bunkers that today can house combat troops by the hundreds.

And thus did Saddam Hussein acquire the technical expertise, the plans and even some of the materials to build a network of bomb shelters and reinforced jet fighter hangers that apparently has protected his troops and air force, and even himself, from one of the most intense aerial assaults in history. U.S. officials concede that the concrete cocoons have allowed Hussein, at a critical time, to maintain control and command of his forces.

In interviews this week, engineers, contractors and material suppliers described for The Times how Hussein over the last decade has borrowed from the world’s best technology to piece together his protective labyrinth--and they made clear that its destruction might be a vexing task.

As one engineer put it, the shelters “are not easily knocked out--because they are designed not to be knocked out.”

The bunkers, they said, range from sophisticated underground command posts designed to protect sensitive electronics gear from repeated aerial attacks to hangars that are even stronger and more bomb-resistant than those built to protect NATO aircraft. At least some employ the same architectural designs that allow buildings to withstand severe earthquakes. They are further concealed by the desert camouflage netting that makes them blend into the background.

That all this was built with the assistance from countries now trying to destroy it is one of the war’s early paradoxes. Western governments now trying to defeat Hussein did nothing to stop the assistance back in the 1980s because they preferred the Iraqi leader to his Iranian counterpart.

“At the time,” said Joe Janssens, an executive with the Brussels-based firm Six Construct, which built some of the bunkers that now stretch across Iraq, “Hussein was a good fellow compared with the ayatollah, who had taken those American hostages.”

“Iraq was fighting Iran,” said Colin Croft, chairman of the Federation of Nuclear Shelter Consultants & Contractors in London, “and we had no idea this would be turned against us.” Croft said his organization supplied Hussein with plans for combat bunkers in hopes that “some of our members would get work.”

“That didn’t happen,” he said, but Hussein ended up with the bunkers anyway.

Various European companies helped Iraq build hundreds of bunkers, part of a nationwide defense construction program that began shortly after Hussein took power in 1979, and a year before he began his war with Iran. While bunkers and bomb shelters have proven effective in many modern wars, Hussein’s fortifications are believed to be among the best ever built.

Pentagon spokesman Pete Williams said Friday that the U.S. military has been gathering information from makers of Iraq’s underground shelters.

“I think our folks have a pretty good sense of what the vulnerabilities are, where the targets should be hit,” he said. “Judging from what I have seen, when they do in fact hit the targets in the right place, they have been very effective.”

The experts who helped build the system, however, say it might not be that easy. In these heavily fortified bunkers--said to combine the amenities of home with computerized communications equipment--Hussein and his staff should be able to withstand virtually any attack by conventional weapons.

Some bunkers, sources said, protect the Scud missiles that Iraq has lobbed at Israel and Saudi Arabia. Others were designed to hold large numbers of combat troops. The Federation of Nuclear Shelter Consultants & Contractors in London designed 40 bunkers for Iraq that could each hold up to 1,200 troops.

“These (plans) were OKd and we didn’t hear anything more until 1986, when we learned that a lot of equipment--pressure doors, ventilation units, blast valves, chemical toilets--were being sent from Switzerland,” said the organization’s Croft. “We are 95% sure that the units were completed in 1986.

“These units were designed to give protection against modern weapons,” he added. “They can be built in a matter of days. A bulldozer digs the hole, takes the sand all out and the unit, like a prefab unit, is dropped in.”

Perhaps the most remarkable aspect of Hussein’s bunker system is in the extensive protection it has apparently provided the Iraqi air force. The construction of bomb shelters becomes more difficult with size, according to experts, and yet Iraq has managed to create a chain of bunkers large enough to protect an estimated 80% of its 800 combat planes.

Iraqi military engineers, working closely with European contractors, have produced an all but impregnable bunker. Western officials who saw the aircraft shelters under construction told The Times that they were most impressed by the density of concrete and creative use of large quantities of packed sand.

To build the crescent-shaped roof and walls of the bunkers, the Iraqis used a layer of concrete about four feet thick, nearly twice the thickness used in NATO’s aircraft shelters. Then a layer of densely packed sand, ranging from six to nine feet thick, was poured on top of the concrete. The bunker doors are made of thick steel with an outer concrete barrier to absorb rocket or missile attacks.

“It’s very difficult to get inside the shelter and destroy the aircraft,” said one Western military expert who has inspected the bunkers. “You need a tremendous amount of ‘smart bombs’ or missiles--at least one to open the door and at least one more to destroy the aircraft. Even with 10,000 or 12,000 bombing sorties, you’re not going to take these out unless you also use cruise missiles or something comparable.

“There are hundreds of these bunkers at airfields all over Iraq, so the amount of weaponry involved in knocking them all out is certainly mind-boggling.”

The bunker system at Iraq’s Beiji air base, about 100 miles north of Baghdad, is illustrative. Iraqi military authorities considered this base so strategic that last year they placed the elite of their prewar hostages--a team of two dozen British military advisers captured in Kuwait--at Beiji’s key facilities during Hussein’s human-shield operation.

Eyewitnesses have counted at least 100 of these reinforced aircraft bunkers scattered around Beiji and, despite several air strikes that have knocked out large sections of the base’s runways and command buildings, the shelters are believed to be largely unscathed.

Inside the shelters, Hussein is believed to have preserved the centerpiece of his aerial armada--about 80 French-built Mirage F-1 fighter jets--as well as the majority of his estimated 26 long-range, Soviet-built SU-24 fighter-bombers.

Using similar bunker technology, Hussein has protected much of his remaining fighter-jet arsenal at two other key bases closer to Baghdad--Balad air base, 30 miles north of the capital, and the Baghdadi base, 50 miles to the north.

That Iraq’s runways have been bombed repeatedly should be of little comfort to the allies, some experts say. Through contractors in France, Iraq acquired materials for rapid temporary repairs that might permit small numbers of takeoffs and landings. The repair kits include fast-hardening concrete and mobile tarmac material that can be quickly rolled out onto a runway and rolled back into a bunker after takeoff or landing.

Other experts have reported seeing several long stretches of highway clearly designed to double as aircraft runways--wide and long enough to accommodate even Iraq’s Soviet-built Ilyushin 76 transport planes.

“If Saddam can get his aircraft to these highways, he’s in business,” a Middle Eastern military expert said.

But to use his aircraft effectively, Hussein’s communications network and supporting computers must also survive. Much of that delicate equipment is now believed to be housed in bunkers that employ the most sophisticated earthquake engineering available.

Whether it is an earthquake or a bomb blast, the key to survival for any building is to keep the shock waves from shaking the structure apart. One technique that has been employed in Iraq is to separate the foundation from the structure itself through an earthquake engineering system called base isolation, according to another expert, who asked not to be identified.

In an earthquake, base isolation allows the foundation to move back and forth beneath the building, absorbing the energy from the quake instead of passing it along to the structure. That same technique has been used in some of Iraq’s underground shelters.

The design, said Uday Patil, a senior engineer with Dames & Moore, substitutes flexibility for brute strength, allowing the facility to “eat up energy” from a bomb.

“A blast generates a lot of energy, and that’s what moves or damages the building,” Patil said. “If you eat up that energy, you are reducing the impact of that energy.”

Said another expert familiar with Iraq’s bunkers: “You dig a hole, build a base isolation system, then drop your shelter on it.” The facility, he said, can be hidden with a concrete slab, covered with sand, and even bombs that hit close by should cause little damage to equipment inside.

While reinforcing bunkers poses one set of difficulties, keeping them hidden presents another--and in this regard it again appears that Hussein received outside help.

One of the trickier problems in keeping a bunker hidden is venting the heat created by people and equipment inside--without pointing attackers to telltale stacks, doors or vents.

“All of these things are heat generators,” said Herbert Saffell, an engineer with the Ralph M. Parsons Co. in Pasadena, who has designed similar facilities. “You’ve got people, computers, electronics equipment, all producing heat, and you’ve got to get rid of the heat.”

The source of the heat can be hidden in an urban environment like Baghdad, because it can be piped elsewhere and blended in with heat produced by benign sources. But in the open countryside, heat vents and entryways are more difficult to conceal.

“These generally are the vulnerable points,” Saffell said. “How are you going to take care of the heat and how are you going to get people in and out?”

People inside the bunkers also need adequate ventilation so they can breathe, leading one expert to offer this scenario for dealing with the shelters: “Seal them up. They make great tombs.”

One way to limit the heat disposal problem is to use many bunkers, thus reducing the amount of heat coming from any one source, and Hussein has no shortage of them.

Camouflage is another solution. The bulk of the bunker can be buried under sand, a material that is abundant in Iraq, of course. But to hide ventilation outlets and entrances, more sophisticated cover is needed.

According to the French company that manufactures fishing nets, Lancelin-Barracuda SA, Iraq purchased millions of dollars worth of customized netting to hide its military facilities. Such nets, it is believed, have been draped over vents and doors.

Inside, the bunkers aren’t necessarily uncomfortable.

“The name ‘bunker’ is misleading,” said Georg Niedermeier, a director of the German company that absorbed the firm that built Hussein’s personal command bunker in Baghdad.

He described the hideaway as “more a cellar than a bunker” and said the large, single-floor enclosure was built under a government guest house near Hussein’s palace. It is equipped to house Hussein and his aides for as long as a year. Niedermeier described it as “very luxurious.”

Dye reported from Los Angeles, Fineman from Amman, Jordan. Contributing to this report were Times staff writers Joel Havemann in Brussels, Tyler Marshall in Bonn and Rone Tempest in Paris and researcher Nina Green in Los Angeles.