THE BENEDICTINE Sisters in Erie, Pa., live by a simple doctrine:

"Serve Him with the good things He has provided." Not the least of these good things, it develops, is gas.

The Benedinctine Sisters have drilled into Devonian shale below the convent grounds and, in the words of Sister Dorothy Stoner, "We have found a good supply. We will have the gas needs of our Motherhouse taken care of for approximately 25 years with that one well." Amen.

The sisters are by no means alone in digging in the backyard for their own natural gas supplies. In Pleasant Grove, Ala., successful exploratory drilling last January has led to on-line production at three local wells, all operated by publicly owned utilities. The gas will go for $2.25 per thousand cubic feet, the same as the national price for new gas discoveries.

The Navajo Indian Utility Authority, in New Mexico's San Juan Basin, plans to drill an exploratory well near Farmington. If successful -- and there's every reason to believe it will be -- the gas produced will power Navajo irrigation equipment, and any surplus will be sold to consumers.

In Trinidad, Colo., where 40 percent of the town's 10,000 population live on fixed incomes, last year's natural gas bill was about $2.5 million. Exploratory drilling for its own gas produced spectacular results, with prospect that Trinidad's publicly owned utility may be able to substitute this production (at less cost) for that provided by commercial pipelines.

And so it goes in Illinois, Indiana, New York, Kentucky, Colorado, Pennsylvania and elsewhere where public institutions and private parties like the Benedictine Sisters are being encouraged, indeed urged, to drill for what is known as "unconventional gas" -- natural gas extracted from coal seams and Devonian shale rather than from usual geological environments.

Every day enough gas from coal mines is vented and burned off to provide all the natural gas needs of a city the size of Pittsburgh. Coal mine safety is a major reason for this burn-off. But another important reason the gas has been wasted is that it has not been economically feasible to produce it and compress it for pipeline transportation onver long distances.

The move today, however, is to pump and consume the gas locally or in nearby areas. This requires little pipeline pressure and, at today's energy prices, unconventional gas now looms as an important element in the U.S. energy battle.

The potential, in fact, is staggering. The Bureau of Mines estimates that some 1,500 trillion cubic feet of gas are trapped in U.S. coal seams and Devonian shale -- six times the gas reported by the natural gas industry in regular proven reserves. (With 1 billion cubic feet of gas equal to the energy of 172 million barrels of oil, this means that if only 15 billion cubic feet of unconventional gas were produced each year, it could -- theoretically -- eliminate our current annual dependence on 2.7 billion gallons of foreign oil.)

The American Public Gas Association (apga), in Vienna, Va., estimates that 6,500 communities are sitting atop large, untapped natural gas resources. The Department of Energy adds that thousands more small businesses and farmer cooperatives are in the same advantageous situation as that of the Benedictine Sisters.

It was, in fact, some Erie businessmen who gave the sisters their gas-drilling idea when the businessmen sought a lease to drill on the convent grounds. The sisters decided that if the businessmen thought they could profit from such a venture, perhaps the gas could be developed for the order without intent to profit. So the sisters sold about $100,000 of their closely held stocks and bonds (just about wiping out their coffers), hired drilling experts and struck gas at about 2,300 feet.

The order had been paying about $20,000 annually for gas, so the project is expected to pay for itself in a few years. "If we have the resources, we shouldn't just sit on them," says Sister Dorothy. "Furthermore, we can set an example for others."

Some interests, of course, are not terribly happy about such examples being set. Indeed, the backyard gas phenomenon sends chills up the spines of some investor-owned utility companies, particularly natural gas pipeline operators.

"They have little cause for fear," says Arie M. Verrips, APGA executive director. "The natural gas displaced by the unconventional gas can be retouted to ther customers. There is plenty of demand for both."

The current fear for public institutions and the consumer-at-large is that in 1985, when gas prices are scheduled to be decontrolled, prices may soar dramatically. Some experts believe the commercial price will jump from the current $2.50 per 1,000 cubic feet nationwide to as high as $10 per 1,000 cubic feet, which will made projects like Trinidad's look even better than they do at present.

That town plans to sell its gas at about $2.25 per 1,000 cubic feet and hold the price line even after decontrol in 1985, "a measure," says Verrips, "most communities can adopt once they are producing from their own resources."

"If communities do not develop these unconventional resources in their own backyards," he adds "then the major utility companies will do it. With no price lid after 1985 it could be a very profitable venture for the energy giants.

"But if more and more communities produce and distribute their own gas, this will not only keep down local utility costs for institutions and consumers, but the emergency of a viable and growing competitor could have the anti-inflationary effect of keeping commercial prices down."

The stimulus for unconventional gas development comes from President Carter's Rural Energy Initiatives Program. Under this effort, the Department of Energy awarded a $3.8 million grant to APGA to demonstrate the commercial feasibility of coalbed and Devonian shale gas produced for local distribution and self-help.

"As far as we have gone," says APGA's Verrips, "there's every indication that the already producing wells, in serveral locations in both Colorado and Alabama, will prove economically feasible."

Where problems appear, they usually are political rather than economic. On one upstate New York city council, for example, a member who believes the program constitutes nationization of a "proprietary" industry has stalled exploratory drilling there for more than a year.

Easements and right-of-ways can be a major roadblock as well. While unconventional gas resources may be located in a community, it does not follow that the community's government owns the land. Requently there are many owners, all of whom must agree to make their land available for exploratory drilling, production and transportation. Even when the land is government- or institution-owned, there may be static from abutters.

Despite this, there is some talk by public administrators of forming "joint publicly owned gas systems," consortia to produce gas in one or more areas and distribute it to several members.

Nobody knows whether such a move would provoke heavy lobbying from investor-owned utilities. Private interests have no problem, of course, when governments provide water, sewer systems, transportation or other services -- so long as they operate in the red. But if public bodies get into ventures which could produce sizable profits, some private company is likely to suggest they are taking one of those unspeakable, unthinkable steps toward "socialism." Gads.

However that issue turns out, there's little doubt that many others will be joining the Benedictine Sisters in searching for the wealth of unconventional gas that may lie beneath their bacyards.