It was a little piece of wilderness that had somehow survived the relentless drive of people to crowd in along the shores of Chesapeake Bay; it was a place where the tiny and rare narrow-mouth frog lived.

The Sierra Club fought for it, but decision-makers said the nation needed energy more than it needed the little piece for wilderness or the tiny frogs. And besides, some of the wilderness would remain and some of the frogs survived in another county.

So it is that in the midst of the wilderness stands a $350-million testament to American technology - a vast field of giant pipes and tanks soon to be filled with millions of cubic feet of liquefied natural gas (LNG).

The site of what could be the set of a science-fiction movie is Cove Point in Calvert County, Md., located on the shores of the Chesapeake about 40 miles south of Annapolis and about 60 miles southeast of Washington.

Cove Point will begin operation in 1978. It will be the nation's first full-scale port for importing LNG and will supply about 4 million customers in portions of seven states, including Maryland, D.C. and Virginia.

Experts say that much experience is needed before they will be sure that plans for the safe handling of LNG are perfected, but nevertheless the Coast Guard must prepare plans for the safe passage of LNG in Chesapeake Bay. It appears certain, officials say, that shipping and traffic patterns in the lower half of the bay will be disrupted.

Fear of LNG began in 1944 when a storage tank in Cleveland accidentally released a large amount of the highly volatile liquid into the surrounding neighborhood. It was ignited and 128 people died.

Liquefied natural gas is ordinary gas chilled to minus 260 degrees Fahrenheit, at which state it can be transported by container rather than by pipeline. Six hundred times as much LNG can be carried in the same space as the same amount of natural gas.

In its liquefied state, the gas looks like ordinary water. But when it is exposed to air at room temperatures, it boils - roiling, spitting and crackling like a packaged inferno. The vapor rises like smoke.

The slightest spark will instantly ignite the vapor into a conflagration, experts say. They maintain, however, that it can exploded only if there is the proper mixture of gas and air in a contained area. The liquid itself does not burn.

Because there have been no major spills of LNG, industry and the Coast Guard can't be positive about the precise effects of such an event. They believe the water it touches would freeze instantly, just as a human being would freeze, but that extensive icing would not occur because of rapid vaporization.

Those who are concerned about the effects of a spill fear that enough LNG hitting the water would create a huge vapor cloud that could be blown ashore or over another ship on the bay.

The LNG industry is sufficiently concerned about the fears of citizens to have opened information offices in Washington. Martin R. Engler, Jr., head of the information office and vice president of the El Paso LNG Co., which will be involved in transporting the LNG to Cove Point, admits the possibility of a major traveling fireball, but says the probability is extremely low.

Engler said that if there was a collision or other accident serious enough to cause a spill, there is a 90 per cent or greater chance that it also would cause a spark or friction of sufficient heat to ignite the resulting LNG vapor. Furthermore, he said, it would vaporize and burn so fast that there wouldn't be time for a wind to blow the vapor cloud very far before it burned out. Contrary to the fears of some that a strong wind would blow the vapor to a populated area, Engler said that a strong wind, even a hurrican, would cause the LNG to vaporize faster and either burn or dissipate into the air.

If the LNG failed to ignite when it was released, it would form into a vapor cloud and drift until it dissipated into the air, or reached a source of fire - a burning cigarette or a pilot light for instance - at which point it would ignite.

Tests are being run at the Naval Weapons Center at China Lake, Calif., and two attempts thus far to set off LNG vapor with an explosion have failed, a Coast Guard spokesman said.

But according to a 1976 Rand Corp. report, the handling of LNG entails "unique hazards of a natural and scope not previously encountered in large-scale transporation of hazardous materials."

"In assessing risks of LNG operations," the Rand report found, "the best we could conclude is that not enough evidence has been collected to prove that it is so unsafe as to warrant its abandonment nor does enough evidence exist to prove its safety."

It is the same dilemma that faces people who have not decided whether to accept the risk of nuclear energy in order to enjoy its benefits.

While it is apparent from descriptions of possible trouble that its potential for disaster isn't in the same league with nuclear power, a major LNG accident could wreak untold havoc, experts maintain.

Industry leaders are convinced, however, that the precautions they are employing in the transportation of the gas will ensure safety to the public in even the most unlikely of potential disasters.

The LNG industry is trying to guarantee against spills with a special fleet of nine LNG tankers being built at a cost of about $100 million each to do nothing but run LNG from Algeria, the exporting nation, to Cove Point and Elba Island, another smaller facility in Georgia not yet open.

While an oil tanker has one hull that itself is the tank, the LNG vessels have double hulls separated by six to eight feet of space. Self-contained tanks are within the hull.

The 930-foot ships, each carrying enough gas to supply 70,000 homes for a year, will dock at a pier built in the Chesapeake about a mile offshore, at the rate of about one every 2 1/2 days. The LNG will be piped ashore through a tunnel and into four gigantic shore tanks. The gas will then be piped to vaporizers that change it back to gas for an 87-mile pipeline trip across Maryland and the Potomac River to Evergreen Mills west of Dulles Airport in Londoun County.

At Evergreen Mills, the pipeline hooks up with the Columbia gas company's main distribution system for delivery to area customers and to Consolidated, a Pittsburgh gas company in on the venture.

LNG is far from being a new commodity. For years, gas companies in the United States have liquefied natural gas from pipelines and stored it for use during peak periods. And the U.S. has even been exporting some LNG from Alaska to Japan, the world's largest LNG user.