With many meteorologists forecasting an unusually cold winter, the United States is heading into the home heating oil season with the smallest reserves in more than two decades, government sources said last week.

But officials of the U.S. Energy Information Administration said that, even though current stocks are 21.6 percent lower that at the same point a year ago, fuel oil supplies should be adequate to meet even above-normal heating demands.

Home heating oil prices, running about 3 cents a gallon less than last winter's average of $1.20 per gallon, are expected to increase to about $1.24 a gallon by the end of the winter.

While the prospect of adequate supplies and relatively stable prices would appear to be good news for consumers, industry sources cautioned that with reserves at a modern low the possibility of localized shortages in some parts of the country cannot be totally discounted, if the winter proves to be unusually severe.

J. Erich Evered, administrator of the energy information agency, said his agency estimated that at current rates of import and production, home heating oil supplies should peak in the weeks just ahead at between 170 million and 180 million barrels.

By comparison, heating oil stocks hit a peak of 207.3 million barrels last September, and the United States entered the winter season with at least 230 million barrels on hand in each of the previous six years. The last time stocks were as low at the start of the heating season was in 1961, when they peaked at 177.9 million barrels, government sources said.

If heating oil stocks reach 180 million barrels this will represent about a 65-day supply at the current rate of consumption. This is down sharply from the 81-day supply on hand two years ago, and also would be the lowest level in more than 20 years.

Nevertheless, Evered said the low level of supply does not necessarily represent a problem "because demand is lower than in the past, and because of the worldwide availability of crude oil and excess refinery capacity."

While the average American house heated by oil used more than 1,200 gallons each year in the 1960s, the combination of conservation and price increases has helped cut the average household's annual consumption to under 842 gallons.

Dr. Edward Murphy, director of statistics for the American Petroleum Institute, noted that oil companies also can keep lower inventories of heating oil than they stockpiled in the past because of excess refining capacity.

"Back in the 1970s, American refineries were operating at over 90 percent of capacity, and 93 percent appears to be about the maximum rate at which most can operate," Murphy said. "So with refineries continually operating at that rate, you didn't have the capacity to increase runs in January to meet a surge in demand for heating oil. If heating oil stocks reach 180 million barrels this will represent about a 65-day supply at the current rate of consumption. This is down sharply from the 81-day supply on hand two years ago, and also would be the lowest level in more than 20 years.

"You don't have that situation now," Murphy added. "We've got 4.7 million barrels of excess refining capacity in the United States at the moment, and with refineries operating at just over 70 percent of capacity, they are in a position to produce extra heating oil very quickly if the demand for it materializes."

The result is that oil companies increasingly are choosing to stockpile crude oil, and refine it into home heating fuel or gasoline only in response to consumer demand. Crude oil stocks, according to the energy information agency, stood at 351.4 million barrels on Sept. 17, only about 2 percent lower than a year ago.

"If we do turn out to have a cold winter, the companies will refine more of that crude into home heating fuel," Murphy said.

The other factor that encouraged oil companies to draw down their stocks earlier this year, and to keep them relatively low, has been the combination of relatively weak demand and the glut of petroleum that has existed for the past year on the world market.

"Carrying inventory in the past couple of years when interest rates have been high and prices have been falling has been a losing proposition," Murphy noted.