They call it a "maxidisaster." There has not been one in recent years, but there could be one this winter or any time: a devastating blizzard, flood or earthquake that paralyzes a large region of the country, killing hundreds and causing a breakdown of local authority.

"We're not adequately prepared for one of those," says William H. Wilcox, chief of the Federal Disaster Assistance Administration. "Hurricane Agnes (in 1972) was the closest, but very few lives were lost because the waters rose so slowly and people were evacuated."

With winter newly arrived, Wilcox and other federal and local officials are worrying about what it might bring. More than 100 people died in last Febraury's severe storms, and 20 have already died in storms during November alone.

Even with the blizzards and 100 deaths, however, last winter was nothing like the "maxidisaster" that haunts Wilcox's imagination.

What he is trying to do is raise the public's awareness of the dangers of winter-dangers that are all too easy to forget.

"What happened (here in Washington) last summer when people hollered so much over a short electrical outage-30 or 40 hours-indicates what a fragile society we are generally," Wilcox said. "The more urban an area is, the more fragile it is likely to be."

The Washington area, Wilcox believes, is particularly fragile because people here are not used to servere winter weather and tend to be ill-prepared for it.

Local governments have worked out an elaborate regional plan for dealing with one ominous possibility-a sudden cutoff of natural gas supplies that heat most of the homes in the Washington area.

Under the plan, nonessential customers would be shut off first as natural gas supplies dwindled. If the "entire utility network" were shut down, the government agencies and the gas companies would work to find alternative fuel supplies and to relocate people in "suitable alternative locations."

In Fairfax County, for example, there are plans for moving people from their cold homes into schools that are heated by oil.

Meanwhile in the District, the mayor would be manning his emergency command center. The D.C. Office of Emergency Preparedness and similar organizations in the surrounding counties would be trying to make sure that food, blankets and other neccessities were available.

All this looks fine on paper. The point that Wilcox wants to make, however, is that these plans can easily break down in severe weather. He thinks people should be prepared for circumstances in which government cannot help and it is every man for himself.

"We suggest that people ought to have an alternative heat source in their homes, although they should be careful of unvented heaters," said Wilcox. "Personally, I'm going to install a wood stove in my fireplace. . . .

"We suggest having on hand plenty of nonperishable, high-energy foods. Preparing for a winter emergency is like preparing for any emergency, and we suggest that people should have a transistor radio and flashlights and a family plan. The family ought to get together and work out ways to deal with an emergency.

"Communities should have a signal system. For example, red cardboard in a window would be a signal that people in a house need to be rescued, that help is needed in there."

Wilcox said the best general family guide to winter preparedness that he has seen is "Winter Survival," a booklet available from the U.S. Department of Energy Technical Information Center, P.O. Box 62, Oak Ridge, Tenn. 37830.

"People shouldn't travel by car when there's a storm threatening if at all possible," said Wilcox. "If you're likely to use your car in bad weather, have a shovel, a bucket of sand and a good strong flashlight in the trunk. Blankets are a good idea, too.

"If the car stalls, it's best to stay inside unless you're in good health, are wearing warm clothing and your destination is visible. Run the motor only intermittently (for warmth). The tail pipe exhaust should be free of snow. The downwind window can be [slightly open] to provide fresh air."

A helpful booklet called "Safe Driving in Winter" is available from the U.S. Department of Transportation's National Highway Traffic Safety Administration, Washington, D.C. 20590.

In addition to safety suggestions, local officials here are dispensing a great deal of information on how to save energy this winter.

Northern Virginians can call (800) 552-383, the free energy hotline of the state office of Emergency and Energy Services, to talk with a specialist about insulation, storm windows and the new federal energy tax credit, and to sign up for a free home "energy audit."

The office is receiving up to 200 calls a day, according to Betty Page, the promotion supervisor there. She said 58,000 packets have been sent out to people who want energy audits. The people fill out forms with imformation about their houses, the information is then analyzed by computer and energy-saving suggestions tailored to individual houses are sent to the occupants.

The office is also running hundreds of energy-saving clinics this winter. Dates and times for them can be obtained through local community colleges.

In Maryland, the free energy hotline is (800) 492-5903.

"Recently we've been deluged with questions about the tax credit," said Janet Shorey, a "conservation coordinator" who works on the hotlines. "People want to know, 'Does this or that qualify? Mainly they wonder about aluminum siding, I hate to tell them, but it doesn't qualify."

The people who do this energy and emergency work seem to enjoy it. They have the sense that they are doing important work, that people care about these matters.

Wilcox, the federal disaster man, talks about how his 160 workers are "called to active duty" when an emergency hits, how they must be part soldier. part social worker, part "cynic"-this last in order to catch disaster victims seeking to get more disaster relief aid and funds than they are entitled to.

"People work seven days a week, 24 hours a day when necessary," said Wilcox. "We get concerned about what we call burning out. It's a kind of a syndrome. After they get back here they collapse. . . A blizzard can close down a whole region. That gets to be very exciting because the damage is so widespread. . . . "