Corporations whose fortunes depend heavily on the price of petroleum may receive a financial lift from falling oil prices, but they aren't about to jettison long-range conservation plans.

In fact -- like consumers rejoicing in lower heating oil and gasoline prices but not ready to rip out home insulation or buy a gas-guzzling 1968 Chrysler Imperial -- corporate executives are reacting somewhat skeptically to falling petroleum prices.

"I doubt very seriously that anyone expects, in a 10-year time frame, anything but rising prices and eventually a scenario of depleting resources," said David K. Barnes, executive vice president of E.I. du Pont de Nemours & Co. "I don't belive you're going to see a great simulus to expansionary investments of one kind or another that are premised solely on a continued drop in oil prices."

Oil users are still looking for ways to cut consumption, and purveyors of energy efficient equipment, for the most part, continue to anticipate expanding markets. Most of the synthetic fuels industry, which wasn't very far along in development when falling prices hit, is on the shelf, but other alternate energy producers are undeterred.

"We have more efficient aircraft on order for delivery this year. We're looking to lower the age of our fleet and continue to bring in new, more efficient aircrat," said Jack Kling, a spokesman for USAir. The company also has 10 more aircraft -- a new, more efficient Boeing model -- scheduled for discovery in 1984, with an option for even more.

In the meantime, lower oil prices are welcome. "A penny a gallon change in the price of oil is a $3 million change because of the amount of fuel we use," King noted. "Last year the airlines realized considerable savings in the decrease in the cost of fuel, but they still cost a considerable amount of money, because discounting ate up the savings. It wasn't enough to put them in the black."

Further savings "might be passed on to the customers in lower fares, or it may offer some airlines the opportunty to make a profit where they've been sustaining a loss for several years," he said.

Producers of more efficient aircraft say they expect sales to hold up. "We've designed these new airplanes when fuel was about 50 cents a gallon, and we're not anywhere near back down to that level," said a spokesman for Boeing.

"Of course, lower fuel prices does make the older airplanes look good, too," he said. But he added, "We haven't changed any of our forecasts or predictions or thoughts about how we're going to operate our business. The companies are still going to have to buy airplanes for growth, and when they buy they're going to buy more efficient planes."

The DC9/Super 80 is certainly the most fuel efficient aircraft in its class, and there has been pressure not only to replace older, less efficient aircraft but there are also a few other qualities that recommend it -- reliability, less outside noise and passenger comfort," said Dave Eastman of McDonnell-Douglas, manufacturer of the aircraft.

Because the new aircraft are 30 to 40 percent more fuel efficient than the equipment they replace, they offer savings even at lower fuel prices, he said. So far, the company has seen no slowdown in orders -- nor does it expect to, he said.

Fuel costs represent 11 to 14 percent of the total costs of railroads. Because trucks and barges use more fuel, those modes of transportation suffered more as fuel costs went up. "There is a greater competitive shift in their favor when oil prices go down, and a greater competitive shift in our favor when prices go up," said Frank Wilner of the American Association of Railroads.

Like the airlines, the railroads are replacing old equipment with more fuel-efficient carriers. In 1981, the industry averaged 246 revenue-ton miles for each gallon of fuel consumed, a 22 percent improvement over 1971, according to Wilner. Using fuel-efficient locomotives, which are gradually replacing older ones, the industry should be able to average more than 600 revenue-ton miles using unit trains on favorable terrain, he said.

There has been a slight slowdown in the shift to more fuel-efficient locomotives, but the change has been caused by the recession rather than the decline in oil prices, he said. "If the price does go down to 77 cents a gallon, the railroad industry is not going to assume that it's going to stay there.The industry is going to continue to replace its stock because we do expect oil prices to go back up again."

The petrochemical industry, a major oil user, expects improvements both from the lower price for raw materials and the stimulative effect on the economy caused by the oil price decline. Du Pont (with the exception of oil company subsidiary Conoco) is a compare where approximately 75 percent of the produt line is hydrocarbon-based and where nearly a third of capacity has been idled by the recession.

"It's very hard to see, from the standpoint of Du Pont, with the exception of Conoco, any real negatives in the price of oil coming down," said Barnes. As the drop in oil prices and the recovery allow Du Pont to use more of its capacity, its high fixed costs will be better offset, allowing profit margins to improve, he said.

Because there is so much unused capacity in the United States and abroad, Barnes said, he does not expect to see spending on new plants for a long time to come.

Energy accounts for about 20 percent of the costs in the steel industry. "Any decline in those costs will be of help to the company, which is very energy-intensive," said Richard E. Storat, manager of corporate energy affairs for Bethlehem Steel. "At most of our locations, Bethlehem can burn oil instead of some natural gas to minimize our total energy costs," he said, noting that the company has already made that switch in several locations.

The steel industry, hard hit by the recession, also expects to fare better to the extent lower energy costs bolster recovery, he noted.

In the automobile industry, the same is generally true. But it is also true that in the automobile industry, where the life of the product is normally somewhat shorter than the life of a locomotive, an aircraft or a factory, the product mix is being altered by the decline in gasoline prices.

Because the industry adjusted its manufacturing capacity, at great expense, to produce small cars designed for maximum fuel efficiency, prices of those cars may decline as big car prices climb because the industry cannot build them fast enough, she said.

Union Oil Co. came to the Capitol late last week and parked another sort of car in front of it. It was a shale oil demonstration car, an Oldsmobile Cutlass Ciera LS fueled and lubricated by products made from oil shale.

Union expects to begin producing 10,000 barrels a day of shale oil later this year at a facility near Parachute, Colo. Union Chairman Fred L. Hartley conceded that falling oil prices have altered projections about the date at which shale oil might become commercially feasible.

Hartley said that the U.S. Synthetic Fuels Corporation wants Union to go forward with additions to the shale oil plant but that to do so will require greater price supports because of the growing gap between the cost of oil from conventional sources and the cost of producing oil from mountains of shale.

If shale oil is produced successfully from the first part of the plant, Union may receive up to $400 million in federal price supports that will make up the difference between the price for a more conventional fuel and the cost of the shale oil. If the company eventually begins making money on the shale oil without the price supports, the government can recoup part of that investment.

"If we don't produce oil, the government doesn't give us anything," said Hartley. "That's a pretty good deal on an experiment of this magnitude."

Hartley was joined by the head of the Synthetic Fuels Corporation and Sen. Henry Jackson (D-Wash.), both of whom urged continuing support for synthetic fuels programs. "The glut is temporary," said Jackson. "It's absolutely foolish to assume the problems we face are going away."

Some would-be producers of alternate energy have withdrawn their bets that oil prices will rise far enough, fast enough to make it worthwhile. Others have hedged.

Officials of Solarex, a Montgomery County manufactuer of photo voltaics, said that their planning and timetable have not really been altered by the downswing in oil prices. While there may be a small drop in sales, most of the industry is aimed at eventually supplying major businesses and utility customers, said a Solarex official.

Those markets were not expected to develop until later on, and by then oil prices may be headed up again. Even current markets are, for the most part, insulated from the impact of lower oil prices.