THE TWO MEN stood in a freezing duck blind on the marshy edge of Chincoteague Inlet, watching the sun set on Assateague Island and, perhaps, the American sporting life.

They were David B. Lombard, a doctor of physics specializing in geothermal exploitation for the Energy Research and Development Administration, and Ronald L. Smith, a master of economics at the Central Intelligence Agency who watches the ebb and flow of the world's energy.

Both are cheerful, friendly fellows whose considered (and unofficial) opinion is that the United States - not to mention the rest of this crowded world - is on the verge of a disastrous energy shortage that will bring an end to our gadgety, gas-guzzling, overheated, throwaway frenzy. Recreation American style, which is to say on wheels, will be among the first casualties, they say.

On days when the numbers they have been contemplating seem particularly bleak they speak thoughtfully of the collapse of civilization. Dramatic efforts might stave off the crisis for a few years, the two scientists said, but there is very little hope for the long term, barring a breakthrough in hydrogen fusion and/or solar energy for which there is very little realistic prospect.

"There isn't enough energy to go around now, and it's going to get worse fast," Smith said. "The United States is the most wasteful of all. Where a match would suffice we use a Roman candle. And then we light both ends."

It all seemed more than a little remote from the vantage point of the duck blind, which overlooked miles of winter-brown marsh and the little icebound town of Chincoteague, where the accents and customs of the 19th Century are only grudgingly giving way to television, trinkets and tourism.

"It's very hard to think about what we do in terms of energy," Lombard said. "We're not used to it, in our culture. We run on cheap oil, from which we have always gotten cheap gasoline, cheap fuel oil, cheap electricity, cheap fertilizer, cheap plastic, cheap synthetic fabrics, cheap power and goods of almost every kind. This whole trip is floating on cheap oil, and the oil we are using in this country now still is cheap, in spite of the recent price rises, compared to what it's really worth."

"Peripheral pleasures will go first," Smith said. "That means no more driving hundreds of miles in inefficient vehicles to get to an airconditioned beach house or climb a mountain or spend a couple of days gunning for birds. Boats, beach buggies, long-distance birding, they're all on the way out. It will make the rationing system of World Warr II seem like a picnic.

"In terms of reasonable use of energy what we are doing now is just a step above burning off gas at the wellhead on the scale of irrationality. However valuable this hunting trip may be in terms of recharging one's psychic batteries, it cannot be justified in a world in which the lights are about to go out."

The discussion was interrupted by guide Cork Mcgee, who pointed out a flight of incoming snow geese the ruminating hunters had overlooked. They missed.

"Every nation, including the Middle East oil producers, is in the same boat, ultimately," Smith continued. "Because we are the richest, and use the most energy, it's going to hit us hardest. In an emerging Asian nation the end of the energy will mean they have to go back to using water buffalo to power their irrigation pumps. In the United States there are perhaps millions of homes where when the power fails they won't be able to open a cna of beans. Assuming that there will be a can of beans to be had."

The scientists spent two hunting days and the duration of a duck dinner trying to translate the cost of the trip into energy units. "This sort of analysis is wretchedly difficult," Lombard said, "because you have to prorate almost everything but the gasoline burned.

"Electricity, for instance: how much more electricity did the motel use in lights and resistance heating because of us, minus the amount we would have used at home and at the office, bearing in mind that both home and office were heated and lighted anyway?

"This hunting trip is actually a fairly trivial example of wastage compared with many other forms of recreation," Lombard said. "It doesn't compare, for instance, with driving around the country in a six-ton 'camper,' and in fact the bottom line is that almost anything you do that's fun uses a whole heck of a lot of energy that just won't be available when people are scrambling to keep the children warm and fed.

"We've been living in a fool's paradise for the past few years, but our luck is runing out. The schools and factories that are closed now because there isn't enough natural gas are just a taste of what's coming."

A cloud of brant, disturbed by a distant helicopter, came winging over the water. Tagging along with a flock that flew close to the blind were four gadwalls, two of which fell from four shots.

The economics are brutal," Smith said, hefting the retrieved birds. "At two shells apiece, plus butter and spices and cooking fuel fr the stove, these two birds probably would be a break-even proposition, if we had rowed to the blind instead of using Mr. McGee's 75-horsepower outboard, and ignoring all the powder and shot we've blown away on misses."

He thought for a moment.

"No, I take it back. If these ducks had fallen into the blind on their own account and we ate them raw, the food energy they contain would be less than the calories our bodies have burned just keeping warm today. If Mr. McGee came out here by himself and shot his limit with his usual skill, he'd probably be ahead of the game, but there are too many of us and we don't shoot well enough."

"The energy analysis of this trip in BTUs or therms or kilowatts is a little too exotic to deal with in any useful fashion," Lombard said. "But since the price of ordinary goods is largely a direct function of the energy it takes to produce them, dollars and cents give a pretty fair approximation. The cost of materials lies principally in the energy it takes to extract to process them. The cost of labor is the amount of money a worker demands in order to buy the goods and services - again essentially energy - he fells he must have to live decently."

A whole lot of doodling ensued. Gasoline for 1,000 miles (two 14-mpg vehicles on a round-trip of 500 miles), came to about 72 gallons, half again the amount refined from a standard 55-gallon barrel of oil. At 58 cents a gallon, $41.76. Other substantial operating costs such as wear, depreciation, taxes, interest and insurance, no less than $50. "And by the end of the decade you'll see gas at well above a dollar a gallon," Smith said.

Lodging and meals, (including many dozen of the last oysters and clams Chincoteague's watermen harvested before their boats were frozen in), around $1.50. Guide fees, $200. Shotgun shells expended, (some of them relatively inexpensive handloads), $15. Totals so far, $456.76. Miscellaneous items and a prorata share of the cost of the weapons and other gear made it reasonable to round the cost off at $500.

The bag for the trip was seven snow geese and eight ducks, which came to $33.33 a bird, or at least $14.28 per pound of edible meat after Smith finished cleaning and cooking them.

"My God," he said, contemplating a forkful of black duck. "Talk about burning the barn to roastthe pig."