Despite a weekend of snow and slush here and in the northeastern states, the nation is in the midst of its warmest winter in more than 40 years, giving Washington residents and most other Americans a bit of a break on their home heating bills.

The weather through Jan. 31, according to the National Oceanic and Atmospheric Administration, was 9 percent warmer than usual nationwide, and 17 percent warmer in the Washington metropolitan area.

The unseasonable temperatures thus far have enabled Americans to save an estimated $1.58 billion by using about 6 percent less oil, natural gas and electricity to heat their homes than if this had been a normal winter, according to the National Environmental Data and Information Service.

Nevertheless, most Americans still are receiving higher heating bills this winter than ever.

Natural gas and electricity prices are up sharply over last year.

Only homeowners who heat with oil--which is selling for about the same price as a year ago--have a chance of being ahead of the game.

But the milder temperatures around the country, government sources agreed, have insulated much of the nation from the impact of heating cost increases.

"If we were having a winter like 1976-77, which was the coldest in recent times, people really would be feeling it," an Energy Department official said.

The milder temperatures also are being viewed with considerable satisfaction by the National Weather Service, which went out on a lonely limb back in November and predicted a warmer than usual winter.

The National Weather Service's long-range forecast was viewed with considerable skepticism at the time, because sun-spot watchers, devotees of the woolly caterpillar and "The Farmer's Almanac" all were calling for an unusually cold winter.

However, the number of heating-degree days on a nationwide basis from July 1 through Jan. 31 was 2,342, according to Frank Quinlan of NOAA's Climatical Data Center in Asheville, N.C.

This figure represents the cumulative number of degrees the mean daily temperature is below 65 degrees Fahrenheit. The heating-degree days figure also means the smaller the number, the warmer the winter.

"This beats the previous warmest winter in the last 40 years, 1946-47, when we had accumulated 2,401 degree days by Jan. 31," Quinlan said. "To find a warmer winter than this one, you probably would have to go back to the winter of 1931-32, which was one of the warmest in U.S. history."

The weather also has been unseasonably warm in the Washington area, but not quite as warm as the winter of 1973-74.

The 2,030 degree days recorded at National Airport through Jan. 31 make this a far milder winter than last year--when Washington had accumulated 2,590 degree days by that date--but not as warm as the winter of 1973-74, which had only 1,891 degree days by Jan. 31.

The weather this winter has been significantly warmer than normal in all parts of the country except for the south-central states of Texas, Louisiana, Oklahoma and Arkansas, where it has been 4 percent colder than usual, and the Rocky Mountain region, which is having a normal winter, according to Henry Warren of NOAA's Assessment and Information Service Center in Columbia, Mo.