You can't be too careful.

James W. Morentz, who runs a disaster consulting business in Rockville and publishes Hazard Monthly, last year held an exercise in which -- theoretically -- he spilled a dangerous virus in the middle of Arlington. Then, using computers, he monitored the performance of police, firefighters and others.

"We gave them about an A-minus," he says.

The exercise was important, Morentz thinks, because viruses are in fact transported through the country on their way from National Institutes of Health research labs in Bethesda to the Centers for Disease Control in Atlanta. "They transport all that stuff in the back of station wagons with no markings. It's bad stuff."

NIH safety director Emmett Barkley says that dangerous "biological materials" are so well packaged that even in an accident, "I don't think it's ever going to be a problem." But planning for the unthinkable problem is exactly what Morentz and 500 disaster professionals from around the country were doing this week at the Washington Convention Center.

"Death and destruction from natural disasters are on the increase," says a flier for their conference, called Emergency '85.

If you think things can't get bad, just listen:

"When I started out in the disaster business, a flood was a flood," said Roy Popkin. "Now it has dioxin in it" along with dozens of other complications.

Popkin, a 40-year disaster veteran who helped Morentz organize the conference, told about a torpedo truck that crashed in San Diego. Traffic came to a standstill. Police called an emergency number on the torpedo crate for eight hours before someone answered.

In a way, he said, the United States has been lucky because there has been no "mass casualty situation" since the Galveston hurricane of 1900, which killed 6,000. Even the famous San Francisco earthquake of 1906 killed only about 500, and the death toll from Hurricane Camille in 1969 -- for all the devastation it caused -- was 256.

That luck may work against disaster planners, said keynote speaker Gilbert White, director emeritus of the Natural Hazards Research Applications and Information Center at the University of Colorado.

"We probably have been more complacent than we should have been," he said. " . . .It may be unfortunate that Three Mile Island was not more serious than it turned out to be."

The Big One, of course, would be nuclear war, but few were talking much about that.

As a practical matter, the Big One for the U.S. might be a California earthquake that could cause billions in damage and 100,000 casualties. Keynote speaker Thomas Reutershan, who is setting up something called the National Disaster Medical System, said that in a few years it will enable rescue workers to move casualties by air from California quake sites to hospitals around the nation.

He said 150 "casualty clearing units," each with 103 medical specialists, would be rushed to the scene.

"We can't kid ourselves into thinking it won't happen here," he said.

According to Morentz, "the hazards scene" has changed greatly in the past decade. No longer is emergency planning dominated by retired colonels with volunteers filling sandbags. Management specialists, mental health personnel, even land-use planners and political scientists have become involved.

Said Popkin: "I've watched this whole field grow like crazy."

In the exhibition hall, Ian Davidson of Sidian Trading Ltd. sat by a bulky polypropylene "Famine Bag" filled with a ton of corn. For $12 each, the Cambridge-educated English inventor said he would deliver the bags anywhere in the world.

"I got into this when I and some associates were asked to move 1.75 million tons of cement from Romania to Baghdad," he explained. The loss rate when delivering in standard 100-pound paper sacks was high, he said, from breakage and theft.

The big bags fill a packaging gap between 100-pound sacks and massive tanker deliveries, according to Davidson.

Grain, flour, milk powder and other food can be moved in the bags, he said. Davidson has developed a "total system" for filling them with product, and transporting them in ships and finally on flatbed trucks into the countryside, where their contents can be emptied via spouts in the bottom.

Davidson is pushing the bags for famine relief in Africa.

"The worst thing you can do with these people is move them into refugee camps," he said. " . . .The rule of moving grain is to take it as far as possible in bulk."

With the "Famine Bag" system, a flatbed truck pulls into the village and people come out with their pots and pans to get grain from the spout. Then the truck moves on.

"Now if the road doesn't go to the village, and often they don't, then of course the main means of transport is camels, and they fill the camel paniers direct from the bags. One truck, 50 camels."

The exhibition hall was filled with sellers pushing products to help avert, cope with, and recover from disaster. Displayed were detoxification tents, antiburn gels, flashers, special knife sharpeners, ambulances, portable bridges and compact power sirens.

Some of these are very nifty items that anyone would want to have around his or her camp, house or garden.

Take the Argo 8, an "all-terrain vehicle" with eight tires that looks like a small tank made into a golf cart. It will go 18 mph on land and 2 mph in calm water, according to Robert Archer, marketing manager for Ontario Drive and Gear Ltd., which sells it.

The model he showed cost $5,700 and had an aluminum overhead frame for holding stretchers. Archer said he sells about 1,000 of the amphibious vehicles a year, mostly to "moose hunters. They love 'em. Just pop your moose in the back."

He added: "Moose don't generally come to the road to get shot."

Two city council members from Caracas, Venezuela, examined lightweight splints for broken bones.

"In Venezuela we are teaching people how to care for themselves in floods, earthquakes and fires," said councilwoman Carmen Pacanins.

Tom E. McClung, an inventor from West Virginia, was showing his new Ibex-I, a heavy, geared box from which a 200-foot steel cable slowly and automatically unwinds, lowering one in a harness -- out, for example, of a window to safety in case of fire.

"You could be unconscious, so somebody could literally throw you out the window in the harness and you'd be okay," McClung said.

The devices, which will soon be in production, will cost $1,000 each. McClung said the cost will come down. Right now, oil companies are eager to buy them for oil rigs, he said. The high cost "makes no difference to them."

A Swedish company, Conplan, was selling nuclear blast shelters, air purification units and so on.

Their representative, Karl I. Hultquist, said there are enough nuclear blast and fallout shelters in Sweden to accommodate 6 million of the country's 8 million population. Hultquist said he was not happy with the traffic by his exhibit.

"The interest is very low. We are a little disappointed."

James A Newman, operations manager of the Riverside County (Calif.) Office of Disaster Preparedness, said that his county stretches 200 miles from Blythe in the east to Riverside and has 777,040 inhabitants.

A recent study shows that an earthquake registering 8.3 on the Richter scale would kill 10,000 and injure 80,000.

Such an earthquake, he said, might start firestorms in the cities. Utilities would go out. Communications would be out. A tidal wave from the Salton Sea could be expected.

The chance of this happening within the next 30 years, he said, is now 60 percent and in eight years this probability will increase to 100 percent.

The earthquake, Newman said, will be "totally catastrophic. It would be the worst disaster in the history of the United States, injuring more people and causing more damage than the Civil War."