A warm winter and strong conservation by motorists and users of heating oil make it increasingly unlikely that Washington motorists will find themselves stuck in long gasoline lines again next summer.

At least two major oil companies, Amoco and Texaco, have already switched refinery operations to emphasize gasoline production rather than heating oil -- something not usually done until March. Sunoco plans to make the switch soon.

"Gasoline supplies should be adequate for the summer if demand restraint continues and if there are no major disruptions of crude oil supplies," an Exxon spokesman said yesterday. The company did not disclose whether it had yet tilted its refinery operations toward gasoline.

Amoco, Texaco, Sunoco and Exxon together supply about 60 percent of the gasoline used in the Washington area. Motorists here and across the country are using about 7 percent less gasoline than they were a year ago.

Those companies, along with Shell, announced yesterday that they will supply stations with slightly more gasoline in February than they did this past month.

But since consumers usually drive more in February than in January, supplies will probably seem just as tight.

This January, the amount of gasoline supplied by the oil companies to the public was less than in any month since February 1975.

"If consumption patterns remain down, there should be adequate supply [this summer], but if consumption goes up again, then it's a question of can we get crude oil and at what price," said Sunoco spokesman Bud Davis.

An Amoco spokesman said there will be "a manageable balance" between gasoline supply and demand this spring -- if everything goes right and there are no big surprises.

Texaco spokesman Ed Williams stated what all these caveats add up to: "I don't think we can ever look forward to a truly 'good' gasoline supply situation, ever again. We just don't see it in the cards."

Still, the gasoline outlook seems better than it did last summer when Washington and other areas suffered from long gas lines and it wasn't clear that there would be enough heating oil together through the winter.

At President Carter's urging, the oil companies produced extra quantities of heating oil last summer and fall so the country would head into winter with large stocks.

Now the winter is well long, and those stocks are still about 10 percent higher than normal, according to the American Petroleum Institute. At the same time, the nation's crude oil stocks are slightly higher than normal and gasoline stocks are about normal.

In the Washington area, heating oil stocks are so high that at least one major local distributor, Steuart Petroleum Co., has enough to make it through the winter even if it didn't receive another drop from its suppliers.

"Inventories are ample for this winter." said Leonard Steuart II, the company's president.

Ironically, when Steuart was filling its huge storage tanks with heating oil last summer, the company paid up to $1.14 a gallon because its supply contracts were linked to soaring world spot market prices.

Recently, that spot price for barge loads of home heating oil was down to 71 cents a gallon, a reflection of the relative supply glut.

Based on what are known as heating degree days, Washington's weather this winter so far has been 6 percent warmer than last year and 24 percent warmer than normal, according to another major local oil distributor, another 7 to 9 percent of heating oil by turning down their thermostats.

Woodson said he has about 5.5 million gallons of oil in stocks -- about 2 million more usual for this time of year.

Edward Murphy, director of statistics for the American Petroleum Institute, said the country could probably make it through the winter even if the weather turned cold and crude oil supplies from the Persian Gulf were cut off since there already is two months worth of oil on its way here from that region.

Despite the adequate supply of heating oil, retail prices continue to soar -- up another 2 cents a gallon in the Washington area in just one week, according to a Washington Post survey of 15 heating oil distributors here.

The average price for a gallon of heating oil was 97.3 cents in Washington yesterday, the survey showed -- a nearly 100 percent increase over the past year. Eleven of the 15 distributors had raised prices during the previous week.

Gasoline prices also continued to climb at many service stations in the Washington area, with industry analysts predicting prices of $1.50 a gallon or higher by the end of the year.