Many people in St. Marys County, Md., have been experiencing considerable discomfort during the cold spell - not because they're cold, but because they're warm.

The source of the warmth has made St. Mary's citizens and government officials warm before, but only under the collar. It is the Steuart Petroleum Co., whose facility at Piney Point on the Potomac River in St. Marys has given citizen and government leaders something to oppose for years.

Now, Steuart has received carefully worded letters of appreciation and the company's arch foes are gritting their teeth and squeezing out accolades that include words like "grateful."

The essence of it is that St. Marys County needed fuel oil to keep them from freezing and Steuart had it. If Steuart officials were tempted to tell St. Marys people to try burning wood, they didn't.

"It was a perfect opportunity to demonstrate what our facility can do," said Len Steuart, a company official.

St. Marys has three fuel oil distributors. Two of them get all their oil brought in by barge. With the Chesapeake Bay and Potomac River clogged with ice, the barges couldn't get through. The distributors saw their reserve supplies dwindle as the cold continued.

The third distributor regularly bought some oil from Steuart, and now asked for more. The other two joined him. Steuart had plenty in its storage tanks and in regular deliveries from tankers that could make it through the ice.

The result so far is that Steuart had sold 2.8 million gallons of fuel oil to people in St. Marys since Jan. 1.

"It is ironic," said Len Steuart.

He says that because the county government and citizens organizations have for years resolutely fought Steuart on every move the company has tried to make to expand its facilities.

Steuart wanted to build an oil refinery. In 1974, the question went to a referendum and Steuart lost by an overwhelming margin.

Steuart now has 26 storage tanks and wants to build two more. The county demanded an environmental impact statement. Steuart challenged its authority and ended up court. The Circuit Court agreed with the county commissioners so Steuart took the case to the Court of Appeals. A decision is pending.

Len Steuart said the last environmental impact statement the firm produced cost $100,000. That was for an extension of the Piney Point pier where the oil tankers dock. After three years of trying, Steuart still doesn't have permit from the U.S. Army Corps of Engineers of build the pier.

The county and citizens oppose the pier.

"We can dock one tanker there now and we want to be able to dock two," Steuart said.

Steuart cites the company's other contributions to St. Mary's County."We employ about 85 people now; payroll is $912,000 per year. We pay $425.000 a year in taxes, primarily real estate and corporate personal property. We think we're good for the county."

Hardly anyone agrees. Says county commission president James M. McKay: "I'm grateful that they were able to supply us with oil, but I'm as much opposed to refineries and other expansion at Piney Point as I ever was. We've got all the water pollution around Maryland that we can handle. You'll notice that our letter of appreciation for their cooperation with the fuel oil was very carefully worded."

Says Jack F. Witten, president of the Potomac River Association of St. Marys County: "It was a happy accident. It was grand to have too much oil traffic in the Bay. They spill oil and we don't like the way they handle it."

Of Steuart, Witten said: "He's a good neighbor as long as there's a buck in it."

Of the demand for an environmental impact statement, Steuart says: "It's nothing more than harassment."

Witten and McKay used very nearly identical language to summarize their views: "The fact that Steuart is supplying us with heating oil is fine, but it doesn't change a thing."