"Dig a 4-foot L-shaped trench in your yard big enough to accommodate your family," intoned the moderator of "Protection Is Possible," a government film on how to survive nuclear war. "If you shelter yourself in your basement, use your workbench, bedroom bureaus and other heavy objects as fort-like protection."

The audience in the high school auditorium greeted the grim advice with hoots of derisive laughter, but the message of the movie and the five federal officials who were showing it was clear: The federal government once again wants people to think about the unthinkable.

Acting on orders from former President Carter that have been reaffirmed by the Reagan administration, the country's 3,300 county civil defense directors are busy drawing up plans that federal officials hope could ensure the survival of 80 percent of the American people in the event of a nuclear war.

To finance the first attempt at systematic planning for nuclear war since the easing of Cold War tensions in the 60s, federal officials, at a time of extensive budget cutting, have increased civil defense spending by 12 percent to $125 million. They make it clear that despite the jokes about soggy biscuits and basement shelters, they are deadly serious about their mission.

"It is a feasible program to relocate and shelter people and survive attack," asserts Pete Frederickson, director of preparedness in the Philadelphia regional office of the Federal Emergency Management Agency (FEMA). "The attempt has to be made."

In most locales, the "Crisis Relocation Plans," as they are called, are being treated as just so much paper generated by what usually is an obscure county agency. But in some places, such as Howard County, whose plan is the prototype for the immediate five-state region, the rejuvenation of civil defense already has become a source of controversy.

Two local citizens groups have asked the county council to subject the plan to a hearing. "It gives the citizens a false sense of security," said Pat Birnie, director of the Howard County Peace Action Community, which sponsored the recent meeting at which "Protection is Possible" was shown.

"The people opposed to the plan are vociferous and organized," said Murray Rommal, deputy civil defense director for the county and author of the plan. "But they're a little naive, burying their heads in the sand and hoping it will go away. Nuclear war is horrible, but it's with us."

Government emergency specialists defend the new planning as a long overdue response to the Soviet Union's emphasis on civil defense.

The new attention began in 1978, when the nation's five civil defense bureaucracies were merged into FEMA. The revamped agency attempts to cover all disasters, not just nuclear holocausts, and opened a new school to teach local officials how to cope with hazards from tornadoes to toxic chemical spills. The new Emergency Management Institute, which took over a defunct women's college in Emmitsburg, Md., began classes last January.

The government's most ambitious undertaking still involves nuclear doomsday, an effort reminiscent of the 1950s glory days of civil defense, when hundreds of bomb shelters were constructed and fallout was a national preoccupation. For civil defense planners that mood has been difficult to recapture.

"Trying to survive a nuclear attack is futile," said Albert Donnay, a member of the Baltimore chapter of the Physicians for Social Responsibility, which helped organize the Howard County meeting. "It's a waste of taxpayers' money to spend time on useless planning."

The plan's detractors want county officials to follow the lead of the Cambridge, Mass., city council, which last March forbid its civil defense director from participating in the relocation plan and other civil defense activities.

Besides criticizing the plan on the philosophical grounds that civil defense is a provocative action that could lead to war, Donnay and other opponents also ridicule its logistics.

Federal officials admit the plans are open to criticism, especially the assumption there would be 72 hours warning before a nuclear attack began. These three days would be needed to carry out the massive relocation of urban dwellers to rural areas and to stock shelters with food, water and medical supplies. Stockpiling of supplies in shelters was discontinued in the early 1970s because of the rancid condition of most materials.

Also, most of the plans in existence are only "mini" versions, which must be expanded into full detail at a later date.

"We know there are holes in it," said Rommal, author of the Howard County plan. "It was put together quickly and is in its infancy." The plan, and those in the six other Maryland counties who have written them, are all of the "mini" variety.

Virginia has two counties with "mini" plans and 25 jurisdictions with full-scale plans, all in the Norfolk area.

John Tomaseski, director of the Hampton, Va., civil preparedness office, concedes, "Frankly, I have serious doubts about the logistics. The problem is so immense, putting autos on the road and evacuating thousands."

Alexandria fire chief Charles Rule puts it bluntly. "We're not equipped to handle mass evacuation. You can't get across the 14th Street bridge at 5 o'clock, let alone in an emergency."

The District of Columbia has a full-scale exit plan for residents due within the year, although it has long-standing strategies for evacuating the mayor, fire and police chief and other city officials into a command center at Lorton.

Sam Jordan, acting deputy director for emergency preparedness in Washington, said despite well-written plans, a major problem in past emergencies is "getting people outside of normal working circumstances to come back to work."

Because of the magnitude of the crisis plans, no rehearsals are scheduled. Many details, such as notifying owners of buildings that their property is considered a shelter, are left until the crisis is announced.

"During the first day, we'd contact all the owners who didn't know their offices would be used," said Robert Lee, administrator of Clarke County civil defense in Berryville, Va. The county plans to use churches, the American Legion, realty offices, and banks to shelter 17,000 evacuees from Montgomery County.

"We would buy food and distribute it to the shelters after people reached them," explained Hal Silvers, director of Prince George's civil defense office. "But we have insufficient shelters in the county to serve everyone, especially west of the Beltway."

A look at the Howard County plan, which is being distributed by federal officials throughout Maryland, Virginia, Pennsylvania and Delaware as an exemplary blueprint, illustrates the real life difficulties of such an evacuation.

Under the plan, the majority of its residents -- 104,000 people -- would pack essential belongings, but leave pets, alcohol and weapons behind after the president declared a nuclear crisis. They would drive on Rte. 70 to Garrett County, Md., and several counties in West Virginia, in the expectation their hosts will shelter them.

Citizens with even-number auto tags are to leave immediately, while those with odd-numbered plates are expected to wait six hours before departure, to help assure that roads are not clogged.

The county traffic engineer is supposed to install traffic counting devices on key exit routes, which will be read and reported hourly during the evacuation. Several gas stations will be ordered to remain open and county employes would be allowed to take over private property if they issued a receipt to the owner and kept a duplicate copy for eventual reimbursement, the report states.

Rommal said he expects only 20 percent of the population to disobey the evacuation procedure, once it is communicated. "If I were Joe Citizen, I'd look for direction from my government in an emergency," he said.

The county's 8,000 residents without cars will report to the nearest school on the second day, along with hospital patients and doctors, to be driven by school bus drivers to West Virginia.

About 2,866 key personnel and their 9,107 dependents will report to emergency shelters in the county, such as the Baltimore and Ohio Railroad tunnel and the Provincial House of the Sisters of Bon Secours, where they would commute to their jobs and obtain food and essential supplies "through retail outlets in the vicinity."

Local grocery stores also would be relied upon by another 12,000 residents in two election districts in the high risk fallout areas who are supposed to remain at home, shoring up their homes with dirt to reduce radiation contamination.

As improbable as some details seem, federal officials support the plans as a first step. "If we do nothing, we're all going to die," said Frederickson, of FEMA. "If we do something, we can save life."

In many jurisdictions, the plans are slow in appearing because of local attitudes. For years, county civil defense officials have complained of wildly changing directives from the federal government. The reorganization, and the current emphasis on relocation planning, is viewed with continued skepticism by many within the profession.

In a survey released after FEMA's first birthday, readers of Hazard Monthly, a trade publication, awarded it a D+ for the state of the nation's preparedness.

Specifically, emergency professionals reported the reorganization has done little to correct their longstanding complaints of civil defense's low visibility, duplication of programs, confusion over responsibilities and poorly trained local coordinators.

"Everyone's hope was once all these different agencies got merged under one umbrella, we'd get a grip on national policy," said Dave Watkins, deputy coordinator of civil defense for the city of Fairfax. "But we still end up with five voices. Maybe this crisis relocation planning is just something else we're being sold on."

Local worries are not deterring federal planners. "There are some aspects of the plans that can be ridiculed," said Frederickson, of FEMA, "but the critics are not representative of the entire population.

"There is an increased emphasis on nuclear planning and it's here to stay."