Washingtonians can expect a mild, somewhat cloudy and distinctly unwhite Christmas this Sunday, the National Weather Service said yesterday.

While this may diasappoint would-be sledders hoping for snow, it is good news for families traveling during the holidays.

The outlook through Monday, Dec. 26, for the Washington metropolitan area as a whole calls for fair to partly cloudy skies with little chance of any kind of precipitation - welcome relief from the last few days of rain. Temperatures should be in the 45- to 55-degree range during the day and in the 30s at night, according to the Weather service.

For travelers going farther afled, the weather service says precipitation along most of the East Coast and eastern Gulf Coast probably will be below normal throughout the holiday weekend. There should be no rain at all in central and southern Florida.

Precipitation, including snow in higher elevations and more northerly latitudes, may occur in moderate or normal amounts, the weather service says, in a broad band from Louisiana and southern Texas northeast through much of Mississippi, Tennessee, Kentucky, Ohio and West Virginia into western Pennsylvania and New York.

Above normal accumulations of snow or rain are expected throughout much of the upper Midwest from the Dakotas to northern Missouri. Moderate to heavy precipitation also is expected throughout the upper Rockies and West Coast region, while the Southwest should be characteristically dry.

As for temperatures, most of the nation is expected to remain somewhat above normal for the season throughout the weekend. Daytime highs should get above 30 degrees in almost all sections except the northernmost tier of midwestern states and the extreme northern portions of New York and New England.

Daytime temperatures should reach 40 degrees or more south of Pennsylvania, the Ohio valley and central plains states and exceed 70 degrees in southern Florida and Texas.

Night-time minimums should range from zero in the extreme northern Midwest to the 50s in southern Florida and Texas. A freeze line is expected to extend from southern Virginia southwestward through western North Carolina, Tennessee and northern Arkansas into western Texas and then loop northward across Arizona and into eastern California.

In the Washington area, the expected mild holiday weekend is being brough t about by the interactions of a low pressure system now over southeastern Canada and a high pressure near the Texas coast, which is due to move into the Atlantic off the southeast U.S. coast today.

These movements are expected to turn winds from a westerly to south-westerly direction, bringing in warmer air from the gulf area.

If Washington's Christmas is not a white one, it will not be unusual. According to weather service records, only 14 of the last 90 Christmases have had measurable snow on the ground.

A little snow fell last Christmas Day, but it left only an unmearusable trace on the ground. The last real white Christmas was in 1969, when 4.3 inches of snow was measured.